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 $32.88   3.222%   $33.9394   $33.94   $33.95   $33.90  
  Purchase #2 $40.59   10.136%   $44.7042   $44.70   $44.70   $44.70  
  Purchase #3 $25.63   7.126%   $27.4564   $27.46   $27.45   $27.50  
  Purchase #4 $191.27   6.198%   $203.1249   $203.12   $203.10   $203.10  
  Purchase #5 $29.65   10.692%   $32.8202   $32.82   $32.80   $32.80  
  Purchase #6 $188.67   9.285%   $206.188   $206.19   $206.20   $206.20  
  Purchase #7 $120.33   4.129%   $125.2984   $125.30   $125.30   $125.30  
  7 purchase totals = $629.02       $673.5315   $673.53   $673.50   $673.50