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 $44.97   4.152%   $46.8372   $46.84   $46.85   $46.80  
  Purchase #2 $75.87   10.531%   $83.8599   $83.86   $83.85   $83.90  
  Purchase #3 $189.34   11.201%   $210.548   $210.55   $210.55   $210.50  
  Purchase #4 $23.41   9.528%   $25.6405   $25.64   $25.65   $25.60  
  Purchase #5 $161.31   5.783%   $170.6386   $170.64   $170.65   $170.60  
  Purchase #6 $137.35   9.501%   $150.3996   $150.40   $150.40   $150.40  
  Purchase #7 $178.77   4.411%   $186.6555   $186.66   $186.65   $186.70  
  7 purchase totals = $811.02       $874.5793   $874.59   $874.60   $874.50