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 $88.31   10.452%   $97.5402   $97.54   $97.55   $97.50  
  Purchase #2 $165.91   7.150%   $177.7726   $177.77   $177.75   $177.80  
  Purchase #3 $57.90   8.534%   $62.8412   $62.84   $62.85   $62.80  
  Purchase #4 $96.53   6.104%   $102.4222   $102.42   $102.40   $102.40  
  Purchase #5 $241.82   6.769%   $258.1888   $258.19   $258.20   $258.20  
  Purchase #6 $82.79   6.708%   $88.3436   $88.34   $88.35   $88.30  
  Purchase #7 $35.47   11.325%   $39.487   $39.49   $39.50   $39.50  
  7 purchase totals = $768.73       $826.5956   $826.59   $826.60   $826.50