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 $94.88   3.303%   $98.0139   $98.01   $98.00   $98.00  
  Purchase #2 $167.91   4.196%   $174.9555   $174.96   $174.95   $175.00  
  Purchase #3 $155.34   8.244%   $168.1462   $168.15   $168.15   $168.10  
  Purchase #4 $95.71   8.517%   $103.8616   $103.86   $103.85   $103.90  
  Purchase #5 $58.38   3.749%   $60.5687   $60.57   $60.55   $60.60  
  Purchase #6 $168.55   6.577%   $179.6355   $179.64   $179.65   $179.60  
  Purchase #7 $127.60   6.472%   $135.8583   $135.86   $135.85   $135.90  
  7 purchase totals = $868.37       $921.0397   $921.05   $921.00   $921.10