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 $60.93   10.227%   $67.1613   $67.16   $67.15   $67.20  
  Purchase #2 $131.31   5.573%   $138.6279   $138.63   $138.65   $138.60  
  Purchase #3 $209.88   7.233%   $225.0606   $225.06   $225.05   $225.10  
  Purchase #4 $166.28   7.302%   $178.4218   $178.42   $178.40   $178.40  
  Purchase #5 $42.73   10.768%   $47.3312   $47.33   $47.35   $47.30  
  Purchase #6 $79.78   9.513%   $87.3695   $87.37   $87.35   $87.40  
  Purchase #7 $192.79   9.110%   $210.3532   $210.35   $210.35   $210.40  
  7 purchase totals = $883.70       $954.3255   $954.32   $954.30   $954.40