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 $224.78   12.543%   $252.9742   $252.97   $252.95   $253.00  
  Purchase #2 $148.93   9.659%   $163.3151   $163.32   $163.30   $163.30  
  Purchase #3 $215.47   7.126%   $230.8244   $230.82   $230.80   $230.80  
  Purchase #4 $76.79   11.764%   $85.8236   $85.82   $85.80   $85.80  
  Purchase #5 $132.69   9.171%   $144.859   $144.86   $144.85   $144.90  
  Purchase #6 $60.57   12.471%   $68.1237   $68.12   $68.10   $68.10  
  Purchase #7 $190.64   6.796%   $203.5959   $203.60   $203.60   $203.60  
  7 purchase totals = $1,049.87       $1,149.5159   $1,149.51   $1,149.40   $1,149.50