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 $62.27   8.201%   $67.3768   $67.38   $67.40   $67.40  
  Purchase #2 $186.34   3.832%   $193.4805   $193.48   $193.50   $193.50  
  Purchase #3 $26.96   13.311%   $30.5486   $30.55   $30.55   $30.50  
  Purchase #4 $5.88   8.410%   $6.3745   $6.37   $6.35   $6.40  
  Purchase #5 $126.94   5.389%   $133.7808   $133.78   $133.80   $133.80  
  Purchase #6 $55.60   9.314%   $60.7786   $60.78   $60.80   $60.80  
  Purchase #7 $225.74   5.499%   $238.1534   $238.15   $238.15   $238.20  
  7 purchase totals = $689.73       $730.4932   $730.49   $730.55   $730.60