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 $236.35   11.549%   $263.6461   $263.65   $263.65   $263.60  
  Purchase #2 $94.29   9.822%   $103.5512   $103.55   $103.55   $103.60  
  Purchase #3 $232.38   7.829%   $250.573   $250.57   $250.55   $250.60  
  Purchase #4 $19.82   7.581%   $21.3226   $21.32   $21.30   $21.30  
  Purchase #5 $184.90   8.139%   $199.949   $199.95   $199.95   $199.90  
  Purchase #6 $216.99   5.213%   $228.3017   $228.30   $228.30   $228.30  
  Purchase #7 $50.60   10.202%   $55.7622   $55.76   $55.75   $55.80  
  7 purchase totals = $1,035.33       $1,123.1058   $1,123.10   $1,123.05   $1,123.10