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 $138.80   9.698%   $152.2608   $152.26   $152.25   $152.30  
  Purchase #2 $202.42   3.487%   $209.4784   $209.48   $209.50   $209.50  
  Purchase #3 $117.33   3.644%   $121.6055   $121.61   $121.60   $121.60  
  Purchase #4 $238.74   12.746%   $269.1698   $269.17   $269.15   $269.20  
  Purchase #5 $174.79   5.867%   $185.0449   $185.04   $185.05   $185.00  
  Purchase #6 $60.28   10.315%   $66.4979   $66.50   $66.50   $66.50  
  Purchase #7 $229.78   13.710%   $261.2828   $261.28   $261.30   $261.30  
  7 purchase totals = $1,162.14       $1,265.3401   $1,265.34   $1,265.35   $1,265.40