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 $245.76   8.756%   $267.2787   $267.28   $267.30   $267.30  
  Purchase #2 $45.98   3.682%   $47.673   $47.67   $47.65   $47.70  
  Purchase #3 $204.76   11.619%   $228.5511   $228.55   $228.55   $228.60  
  Purchase #4 $30.94   13.285%   $35.0504   $35.05   $35.05   $35.10  
  Purchase #5 $46.60   12.711%   $52.5233   $52.52   $52.50   $52.50  
  Purchase #6 $93.91   8.614%   $101.9994   $102.00   $102.00   $102.00  
  Purchase #7 $51.94   3.176%   $53.5896   $53.59   $53.60   $53.60  
  7 purchase totals = $719.89       $786.6655   $786.66   $786.65   $786.80