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 $126.77   11.227%   $141.0025   $141.00   $141.00   $141.00  
  Purchase #2 $144.39   11.454%   $160.9284   $160.93   $160.95   $160.90  
  Purchase #3 $231.61   9.329%   $253.2169   $253.22   $253.20   $253.20  
  Purchase #4 $70.86   8.361%   $76.7846   $76.78   $76.80   $76.80  
  Purchase #5 $47.38   11.220%   $52.696   $52.70   $52.70   $52.70  
  Purchase #6 $111.74   3.573%   $115.7325   $115.73   $115.75   $115.70  
  Purchase #7 $68.67   9.753%   $75.3674   $75.37   $75.35   $75.40  
  7 purchase totals = $801.42       $875.7283   $875.73   $875.75   $875.70