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 $63.88   7.461%   $68.6461   $68.65   $68.65   $68.60  
  Purchase #2 $241.93   12.774%   $272.8341   $272.83   $272.85   $272.80  
  Purchase #3 $83.49   10.710%   $92.4318   $92.43   $92.45   $92.40  
  Purchase #4 $11.70   12.330%   $13.1426   $13.14   $13.15   $13.10  
  Purchase #5 $241.85   13.245%   $273.883   $273.88   $273.90   $273.90  
  Purchase #6 $93.36   9.249%   $101.9949   $101.99   $102.00   $102.00  
  Purchase #7 $109.70   8.146%   $118.6362   $118.64   $118.65   $118.60  
  7 purchase totals = $845.91       $941.5687   $941.56   $941.65   $941.40