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 $58.38   10.104%   $64.2787   $64.28   $64.30   $64.30  
  Purchase #2 $192.85   3.615%   $199.8215   $199.82   $199.80   $199.80  
  Purchase #3 $23.49   5.128%   $24.6946   $24.69   $24.70   $24.70  
  Purchase #4 $29.69   10.301%   $32.7484   $32.75   $32.75   $32.70  
  Purchase #5 $216.28   11.271%   $240.6569   $240.66   $240.65   $240.70  
  Purchase #6 $144.64   5.497%   $152.5909   $152.59   $152.60   $152.60  
  Purchase #7 $220.66   3.422%   $228.211   $228.21   $228.20   $228.20  
  7 purchase totals = $885.99       $943.0020   $943.00   $943.00   $943.00