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 $219.38   4.386%   $229.002   $229.00   $229.00   $229.00  
  Purchase #2 $49.77   3.408%   $51.4662   $51.47   $51.45   $51.50  
  Purchase #3 $58.67   11.341%   $65.3238   $65.32   $65.30   $65.30  
  Purchase #4 $231.72   12.860%   $261.5192   $261.52   $261.50   $261.50  
  Purchase #5 $180.25   12.640%   $203.0336   $203.03   $203.05   $203.00  
  Purchase #6 $59.39   13.584%   $67.4575   $67.46   $67.45   $67.50  
  Purchase #7 $106.78   9.456%   $116.8771   $116.88   $116.90   $116.90  
  7 purchase totals = $905.96       $994.6794   $994.68   $994.65   $994.70