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 $75.96   11.268%   $84.5192   $84.52   $84.50   $84.50  
  Purchase #2 $76.95   13.259%   $87.1528   $87.15   $87.15   $87.20  
  Purchase #3 $204.89   5.403%   $215.9602   $215.96   $215.95   $216.00  
  Purchase #4 $232.76   8.750%   $253.1265   $253.13   $253.15   $253.10  
  Purchase #5 $246.47   3.834%   $255.9197   $255.92   $255.90   $255.90  
  Purchase #6 $91.74   4.180%   $95.5747   $95.57   $95.55   $95.60  
  Purchase #7 $246.95   11.535%   $275.4357   $275.44   $275.45   $275.40  
  7 purchase totals = $1,175.72       $1,267.6888   $1,267.69   $1,267.65   $1,267.70