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 $48.40   12.119%   $54.2656   $54.27   $54.25   $54.30  
  Purchase #2 $217.52   3.429%   $224.9788   $224.98   $225.00   $225.00  
  Purchase #3 $87.48   11.226%   $97.3005   $97.30   $97.30   $97.30  
  Purchase #4 $125.62   8.437%   $136.2186   $136.22   $136.20   $136.20  
  Purchase #5 $169.27   8.735%   $184.0557   $184.06   $184.05   $184.10  
  Purchase #6 $95.25   12.741%   $107.3858   $107.39   $107.40   $107.40  
  Purchase #7 $202.58   3.552%   $209.7756   $209.78   $209.80   $209.80  
  7 purchase totals = $946.12       $1,013.9806   $1,014.00   $1,014.00   $1,014.10