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   12.595%   $70.1129   $70.11   $70.10   $70.10  
  Purchase #2 $94.82   8.344%   $102.7318   $102.73   $102.75   $102.70  
  Purchase #3 $150.25   5.191%   $158.0495   $158.05   $158.05   $158.00  
  Purchase #4 $25.54   3.266%   $26.3741   $26.37   $26.35   $26.40  
  Purchase #5 $156.59   3.612%   $162.246   $162.25   $162.25   $162.20  
  Purchase #6 $85.93   11.431%   $95.7527   $95.75   $95.75   $95.80  
  Purchase #7 $203.41   9.529%   $222.7929   $222.79   $222.80   $222.80  
  7 purchase totals = $778.81       $838.0599   $838.05   $838.05   $838.00