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 $108.96   5.229%   $114.6575   $114.66   $114.65   $114.70  
  Purchase #2 $206.86   7.198%   $221.7498   $221.75   $221.75   $221.70  
  Purchase #3 $238.47   8.141%   $257.8838   $257.88   $257.90   $257.90  
  Purchase #4 $23.28   9.269%   $25.4378   $25.44   $25.45   $25.40  
  Purchase #5 $54.62   9.488%   $59.8023   $59.80   $59.80   $59.80  
  Purchase #6 $220.88   11.581%   $246.4601   $246.46   $246.45   $246.50  
  Purchase #7 $13.96   9.852%   $15.3353   $15.34   $15.35   $15.30  
  7 purchase totals = $867.03       $941.3266   $941.33   $941.35   $941.30