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 $205.58   10.122%   $226.3888   $226.39   $226.40   $226.40  
  Purchase #2 $190.67   11.562%   $212.7153   $212.72   $212.70   $212.70  
  Purchase #3 $118.52   6.275%   $125.9571   $125.96   $125.95   $126.00  
  Purchase #4 $75.47   11.170%   $83.9   $83.90   $83.90   $83.90  
  Purchase #5 $209.28   6.352%   $222.5735   $222.57   $222.55   $222.60  
  Purchase #6 $18.55   8.429%   $20.1136   $20.11   $20.10   $20.10  
  Purchase #7 $169.68   4.319%   $177.0085   $177.01   $177.00   $177.00  
  7 purchase totals = $987.75       $1,068.6568   $1,068.66   $1,068.60   $1,068.70