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 $81.96   13.427%   $92.9648   $92.96   $92.95   $93.00  
  Purchase #2 $68.54   13.149%   $77.5523   $77.55   $77.55   $77.60  
  Purchase #3 $157.49   3.314%   $162.7092   $162.71   $162.70   $162.70  
  Purchase #4 $221.54   3.507%   $229.3094   $229.31   $229.30   $229.30  
  Purchase #5 $132.85   9.203%   $145.0762   $145.08   $145.10   $145.10  
  Purchase #6 $77.36   9.740%   $84.8949   $84.89   $84.90   $84.90  
  Purchase #7 $125.41   6.117%   $133.0813   $133.08   $133.10   $133.10  
  7 purchase totals = $865.15       $925.5881   $925.58   $925.60   $925.70