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 $245.97   7.474%   $264.3538   $264.35   $264.35   $264.40  
  Purchase #2 $173.29   8.800%   $188.5395   $188.54   $188.55   $188.50  
  Purchase #3 $54.31   8.609%   $58.9855   $58.99   $59.00   $59.00  
  Purchase #4 $59.71   5.200%   $62.8149   $62.81   $62.80   $62.80  
  Purchase #5 $171.67   12.488%   $193.1081   $193.11   $193.10   $193.10  
  Purchase #6 $138.82   8.366%   $150.4337   $150.43   $150.45   $150.40  
  Purchase #7 $104.96   11.424%   $116.9506   $116.95   $116.95   $117.00  
  7 purchase totals = $948.73       $1,035.1861   $1,035.18   $1,035.20   $1,035.20