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 $55.80   6.768%   $59.5765   $59.58   $59.60   $59.60  
  Purchase #2 $218.62   8.218%   $236.5862   $236.59   $236.60   $236.60  
  Purchase #3 $194.48   4.713%   $203.6458   $203.65   $203.65   $203.60  
  Purchase #4 $68.70   5.317%   $72.3528   $72.35   $72.35   $72.40  
  Purchase #5 $63.65   12.827%   $71.8144   $71.81   $71.80   $71.80  
  Purchase #6 $61.41   8.716%   $66.7625   $66.76   $66.75   $66.80  
  Purchase #7 $45.54   12.853%   $51.3933   $51.39   $51.40   $51.40  
  7 purchase totals = $708.20       $762.1315   $762.13   $762.15   $762.20