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 $178.50   7.375%   $191.6644   $191.66   $191.65   $191.70  
  Purchase #2 $110.26   11.226%   $122.6378   $122.64   $122.65   $122.60  
  Purchase #3 $56.43   10.791%   $62.5194   $62.52   $62.50   $62.50  
  Purchase #4 $46.38   10.828%   $51.402   $51.40   $51.40   $51.40  
  Purchase #5 $154.52   11.735%   $172.6529   $172.65   $172.65   $172.70  
  Purchase #6 $163.44   8.794%   $177.8129   $177.81   $177.80   $177.80  
  Purchase #7 $147.61   11.584%   $164.7091   $164.71   $164.70   $164.70  
  7 purchase totals = $857.14       $943.3985   $943.39   $943.35   $943.40