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 $67.79   8.756%   $73.7257   $73.73   $73.75   $73.70  
  Purchase #2 $157.92   13.504%   $179.2455   $179.25   $179.25   $179.20  
  Purchase #3 $235.73   3.222%   $243.3252   $243.33   $243.35   $243.30  
  Purchase #4 $162.42   8.570%   $176.3394   $176.34   $176.35   $176.30  
  Purchase #5 $22.51   13.279%   $25.4991   $25.50   $25.50   $25.50  
  Purchase #6 $120.67   10.691%   $133.5708   $133.57   $133.55   $133.60  
  Purchase #7 $245.75   6.574%   $261.9056   $261.91   $261.90   $261.90  
  7 purchase totals = $1,012.79       $1,093.6113   $1,093.63   $1,093.65   $1,093.50