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 $177.95   8.608%   $193.2679   $193.27   $193.25   $193.30  
  Purchase #2 $245.49   3.491%   $254.0601   $254.06   $254.05   $254.10  
  Purchase #3 $55.57   9.230%   $60.6991   $60.70   $60.70   $60.70  
  Purchase #4 $116.50   12.808%   $131.4213   $131.42   $131.40   $131.40  
  Purchase #5 $40.51   12.356%   $45.5154   $45.52   $45.50   $45.50  
  Purchase #6 $202.99   12.395%   $228.1506   $228.15   $228.15   $228.20  
  Purchase #7 $82.40   7.233%   $88.36   $88.36   $88.35   $88.40  
  7 purchase totals = $921.41       $1,001.4744   $1,001.48   $1,001.40   $1,001.60