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 $61.77   4.659%   $64.6479   $64.65   $64.65   $64.60  
  Purchase #2 $204.97   13.364%   $232.3622   $232.36   $232.35   $232.40  
  Purchase #3 $33.74   6.556%   $35.952   $35.95   $35.95   $36.00  
  Purchase #4 $65.47   6.414%   $69.6692   $69.67   $69.65   $69.70  
  Purchase #5 $193.61   4.177%   $201.6971   $201.70   $201.70   $201.70  
  Purchase #6 $89.62   9.293%   $97.9484   $97.95   $97.95   $97.90  
  Purchase #7 $112.74   7.379%   $121.0591   $121.06   $121.05   $121.10  
  7 purchase totals = $761.92       $823.3359   $823.34   $823.30   $823.40