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 $230.35   6.831%   $246.0852   $246.09   $246.10   $246.10  
  Purchase #2 $71.42   4.129%   $74.3689   $74.37   $74.35   $74.40  
  Purchase #3 $57.48   8.758%   $62.5141   $62.51   $62.50   $62.50  
  Purchase #4 $95.30   6.123%   $101.1352   $101.14   $101.15   $101.10  
  Purchase #5 $241.61   4.743%   $253.0696   $253.07   $253.05   $253.10  
  Purchase #6 $61.39   8.771%   $66.7745   $66.77   $66.75   $66.80  
  Purchase #7 $160.46   3.207%   $165.606   $165.61   $165.60   $165.60  
  7 purchase totals = $918.01       $969.5535   $969.56   $969.50   $969.60