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 $111.46   4.234%   $116.1792   $116.18   $116.20   $116.20  
  Purchase #2 $11.38   11.477%   $12.6861   $12.69   $12.70   $12.70  
  Purchase #3 $71.34   3.515%   $73.8476   $73.85   $73.85   $73.80  
  Purchase #4 $225.74   9.152%   $246.3997   $246.40   $246.40   $246.40  
  Purchase #5 $110.35   13.449%   $125.191   $125.19   $125.20   $125.20  
  Purchase #6 $85.88   8.541%   $93.215   $93.22   $93.20   $93.20  
  Purchase #7 $82.58   12.142%   $92.6069   $92.61   $92.60   $92.60  
  7 purchase totals = $698.73       $760.1255   $760.14   $760.15   $760.10