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 $126.75   4.789%   $132.8201   $132.82   $132.80   $132.80  
  Purchase #2 $192.54   5.761%   $203.6322   $203.63   $203.65   $203.60  
  Purchase #3 $204.74   3.379%   $211.6582   $211.66   $211.65   $211.70  
  Purchase #4 $59.83   5.314%   $63.0094   $63.01   $63.00   $63.00  
  Purchase #5 $54.62   6.191%   $58.0015   $58.00   $58.00   $58.00  
  Purchase #6 $84.64   8.594%   $91.914   $91.91   $91.90   $91.90  
  Purchase #7 $7.96   12.167%   $8.9285   $8.93   $8.95   $8.90  
  7 purchase totals = $731.08       $769.9639   $769.96   $769.95   $769.90