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 $85.85   9.698%   $94.1757   $94.18   $94.20   $94.20  
  Purchase #2 $188.51   7.303%   $202.2769   $202.28   $202.30   $202.30  
  Purchase #3 $125.30   10.614%   $138.5993   $138.60   $138.60   $138.60  
  Purchase #4 $16.57   11.194%   $18.4248   $18.42   $18.40   $18.40  
  Purchase #5 $220.78   5.102%   $232.0442   $232.04   $232.05   $232.00  
  Purchase #6 $201.48   12.439%   $226.5421   $226.54   $226.55   $226.50  
  Purchase #7 $11.82   9.672%   $12.9632   $12.96   $12.95   $13.00  
  7 purchase totals = $850.31       $925.0262   $925.02   $925.05   $925.00