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 $85.47   11.222%   $95.0614   $95.06   $95.05   $95.10  
  Purchase #2 $58.85   10.117%   $64.8039   $64.80   $64.80   $64.80  
  Purchase #3 $106.92   5.192%   $112.4713   $112.47   $112.45   $112.50  
  Purchase #4 $68.59   13.406%   $77.7852   $77.79   $77.80   $77.80  
  Purchase #5 $217.49   10.585%   $240.5113   $240.51   $240.50   $240.50  
  Purchase #6 $29.36   7.415%   $31.537   $31.54   $31.55   $31.50  
  Purchase #7 $240.82   8.718%   $261.8147   $261.81   $261.80   $261.80  
  7 purchase totals = $807.50       $883.9848   $883.98   $883.95   $884.00