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 $30.80   12.202%   $34.5582   $34.56   $34.55   $34.60  
  Purchase #2 $106.97   8.305%   $115.8539   $115.85   $115.85   $115.90  
  Purchase #3 $212.61   7.699%   $228.9788   $228.98   $229.00   $229.00  
  Purchase #4 $32.76   13.303%   $37.1181   $37.12   $37.10   $37.10  
  Purchase #5 $85.68   13.274%   $97.0532   $97.05   $97.05   $97.10  
  Purchase #6 $43.82   10.532%   $48.4351   $48.44   $48.45   $48.40  
  Purchase #7 $187.85   8.400%   $203.6294   $203.63   $203.65   $203.60  
  7 purchase totals = $700.49       $765.6267   $765.63   $765.65   $765.70