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 $225.79   5.638%   $238.52   $238.52   $238.50   $238.50  
  Purchase #2 $29.37   11.217%   $32.6644   $32.66   $32.65   $32.70  
  Purchase #3 $229.37   7.498%   $246.5682   $246.57   $246.55   $246.60  
  Purchase #4 $250.61   13.819%   $285.2418   $285.24   $285.25   $285.20  
  Purchase #5 $238.68   11.870%   $267.0113   $267.01   $267.00   $267.00  
  Purchase #6 $190.67   13.826%   $217.032   $217.03   $217.05   $217.00  
  Purchase #7 $85.45   11.507%   $95.2827   $95.28   $95.30   $95.30  
  7 purchase totals = $1,249.94       $1,382.3204   $1,382.31   $1,382.30   $1,382.30