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 $247.65   6.562%   $263.9008   $263.90   $263.90   $263.90  
  Purchase #2 $55.96   11.288%   $62.2768   $62.28   $62.30   $62.30  
  Purchase #3 $171.45   3.560%   $177.5536   $177.55   $177.55   $177.60  
  Purchase #4 $198.86   6.828%   $212.4382   $212.44   $212.45   $212.40  
  Purchase #5 $121.79   8.497%   $132.1385   $132.14   $132.15   $132.10  
  Purchase #6 $210.67   10.313%   $232.3964   $232.40   $232.40   $232.40  
  Purchase #7 $85.34   9.719%   $93.6342   $93.63   $93.65   $93.60  
  7 purchase totals = $1,091.72       $1,174.3385   $1,174.34   $1,174.40   $1,174.30