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 $108.65   10.212%   $119.7453   $119.75   $119.75   $119.70  
  Purchase #2 $118.75   8.656%   $129.029   $129.03   $129.05   $129.00  
  Purchase #3 $8.82   13.806%   $10.0377   $10.04   $10.05   $10.00  
  Purchase #4 $233.96   7.131%   $250.6437   $250.64   $250.65   $250.60  
  Purchase #5 $32.88   3.211%   $33.9358   $33.94   $33.95   $33.90  
  Purchase #6 $243.70   11.234%   $271.0773   $271.08   $271.10   $271.10  
  Purchase #7 $124.79   11.680%   $139.3655   $139.37   $139.35   $139.40  
  7 purchase totals = $871.55       $953.8343   $953.85   $953.90   $953.70