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 $63.33   3.590%   $65.6035   $65.60   $65.60   $65.60  
  Purchase #2 $235.28   8.482%   $255.2364   $255.24   $255.25   $255.20  
  Purchase #3 $153.27   8.167%   $165.7876   $165.79   $165.80   $165.80  
  Purchase #4 $73.53   12.844%   $82.9742   $82.97   $82.95   $83.00  
  Purchase #5 $175.42   12.758%   $197.8001   $197.80   $197.80   $197.80  
  Purchase #6 $214.27   10.574%   $236.9269   $236.93   $236.95   $236.90  
  Purchase #7 $6.93   4.193%   $7.2206   $7.22   $7.20   $7.20  
  7 purchase totals = $922.03       $1,011.5493   $1,011.55   $1,011.55   $1,011.50