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 $238.26   13.197%   $269.7032   $269.70   $269.70   $269.70  
  Purchase #2 $44.30   13.614%   $50.331   $50.33   $50.35   $50.30  
  Purchase #3 $23.39   5.354%   $24.6423   $24.64   $24.65   $24.60  
  Purchase #4 $111.53   12.186%   $125.121   $125.12   $125.10   $125.10  
  Purchase #5 $245.89   10.863%   $272.601   $272.60   $272.60   $272.60  
  Purchase #6 $104.54   10.834%   $115.8659   $115.87   $115.85   $115.90  
  Purchase #7 $16.34   8.320%   $17.6995   $17.70   $17.70   $17.70  
  7 purchase totals = $784.25       $875.9639   $875.96   $875.95   $875.90