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 $84.84   11.379%   $94.4939   $94.49   $94.50   $94.50  
  Purchase #2 $125.93   7.297%   $135.1191   $135.12   $135.10   $135.10  
  Purchase #3 $199.57   9.809%   $219.1458   $219.15   $219.15   $219.10  
  Purchase #4 $169.77   12.503%   $190.9963   $191.00   $191.00   $191.00  
  Purchase #5 $118.68   11.317%   $132.111   $132.11   $132.10   $132.10  
  Purchase #6 $232.52   13.749%   $264.4892   $264.49   $264.50   $264.50  
  Purchase #7 $23.70   13.173%   $26.822   $26.82   $26.80   $26.80  
  7 purchase totals = $955.01       $1,063.1773   $1,063.18   $1,063.15   $1,063.10