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 $55.57   6.564%   $59.2176   $59.22   $59.20   $59.20  
  Purchase #2 $217.78   4.168%   $226.8571   $226.86   $226.85   $226.90  
  Purchase #3 $245.58   10.634%   $271.695   $271.70   $271.70   $271.70  
  Purchase #4 $101.46   5.689%   $107.2321   $107.23   $107.25   $107.20  
  Purchase #5 $93.92   10.127%   $103.4313   $103.43   $103.45   $103.40  
  Purchase #6 $91.85   3.652%   $95.2044   $95.20   $95.20   $95.20  
  Purchase #7 $134.43   10.392%   $148.4   $148.40   $148.40   $148.40  
  7 purchase totals = $940.59       $1,012.0375   $1,012.04   $1,012.05   $1,012.00