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 $88.99   3.606%   $92.199   $92.20   $92.20   $92.20  
  Purchase #2 $22.79   12.553%   $25.6508   $25.65   $25.65   $25.70  
  Purchase #3 $134.60   11.594%   $150.2055   $150.21   $150.20   $150.20  
  Purchase #4 $192.43   12.447%   $216.3818   $216.38   $216.40   $216.40  
  Purchase #5 $104.94   3.612%   $108.7304   $108.73   $108.75   $108.70  
  Purchase #6 $236.58   10.607%   $261.674   $261.67   $261.65   $261.70  
  Purchase #7 $183.36   7.359%   $196.8535   $196.85   $196.85   $196.90  
  7 purchase totals = $963.69       $1,051.6950   $1,051.69   $1,051.70   $1,051.80