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 $24.38   5.557%   $25.7348   $25.73   $25.75   $25.70  
  Purchase #2 $218.75   6.137%   $232.1747   $232.17   $232.15   $232.20  
  Purchase #3 $29.77   4.300%   $31.0501   $31.05   $31.05   $31.10  
  Purchase #4 $160.87   12.417%   $180.8452   $180.85   $180.85   $180.80  
  Purchase #5 $249.87   5.471%   $263.5404   $263.54   $263.55   $263.50  
  Purchase #6 $245.58   9.319%   $268.4656   $268.47   $268.45   $268.50  
  Purchase #7 $231.89   12.777%   $261.5186   $261.52   $261.50   $261.50  
  7 purchase totals = $1,161.11       $1,263.3294   $1,263.33   $1,263.30   $1,263.30