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 $114.46   3.344%   $118.2875   $118.29   $118.30   $118.30  
  Purchase #2 $238.66   10.604%   $263.9675   $263.97   $263.95   $264.00  
  Purchase #3 $51.44   9.127%   $56.1349   $56.13   $56.15   $56.10  
  Purchase #4 $53.26   10.275%   $58.7325   $58.73   $58.75   $58.70  
  Purchase #5 $138.33   11.520%   $154.2656   $154.27   $154.25   $154.30  
  Purchase #6 $119.60   5.769%   $126.4997   $126.50   $126.50   $126.50  
  Purchase #7 $144.43   5.396%   $152.2234   $152.22   $152.20   $152.20  
  7 purchase totals = $860.18       $930.1111   $930.11   $930.10   $930.10