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 $78.81   12.417%   $88.5958   $88.60   $88.60   $88.60  
  Purchase #2 $232.31   12.585%   $261.5462   $261.55   $261.55   $261.50  
  Purchase #3 $209.51   5.861%   $221.7894   $221.79   $221.80   $221.80  
  Purchase #4 $234.48   5.665%   $247.7633   $247.76   $247.75   $247.80  
  Purchase #5 $57.71   11.771%   $64.503   $64.50   $64.50   $64.50  
  Purchase #6 $55.92   9.109%   $61.0138   $61.01   $61.00   $61.00  
  Purchase #7 $121.95   6.191%   $129.4999   $129.50   $129.50   $129.50  
  7 purchase totals = $990.69       $1,074.7114   $1,074.71   $1,074.70   $1,074.70