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 $106.89   10.717%   $118.3454   $118.35   $118.35   $118.30  
  Purchase #2 $218.42   5.853%   $231.2041   $231.20   $231.20   $231.20  
  Purchase #3 $119.88   10.832%   $132.8654   $132.87   $132.85   $132.90  
  Purchase #4 $133.60   3.735%   $138.59   $138.59   $138.60   $138.60  
  Purchase #5 $65.41   4.315%   $68.2324   $68.23   $68.25   $68.20  
  Purchase #6 $114.77   11.824%   $128.3404   $128.34   $128.35   $128.30  
  Purchase #7 $199.28   4.420%   $208.0882   $208.09   $208.10   $208.10  
  7 purchase totals = $958.25       $1,025.6659   $1,025.67   $1,025.70   $1,025.60