Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $148.95   7.521%   $160.1525   $160.15   $160.15   $160.20  
  Purchase #2 $181.98   11.688%   $203.2498   $203.25   $203.25   $203.20  
  Purchase #3 $153.96   4.243%   $160.4925   $160.49   $160.50   $160.50  
  Purchase #4 $134.28   7.384%   $144.1952   $144.20   $144.20   $144.20  
  Purchase #5 $174.68   10.849%   $193.631   $193.63   $193.65   $193.60  
  Purchase #6 $95.60   11.380%   $106.4793   $106.48   $106.50   $106.50  
  Purchase #7 $191.95   13.252%   $217.3872   $217.39   $217.40   $217.40  
  7 purchase totals = $1,081.40       $1,185.5875   $1,185.59   $1,185.65   $1,185.60