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 $232.61   12.224%   $261.0442   $261.04   $261.05   $261.00  
  Purchase #2 $165.37   4.648%   $173.0564   $173.06   $173.05   $173.10  
  Purchase #3 $16.30   5.565%   $17.2071   $17.21   $17.20   $17.20  
  Purchase #4 $121.56   8.729%   $132.171   $132.17   $132.15   $132.20  
  Purchase #5 $42.28   13.163%   $47.8453   $47.85   $47.85   $47.80  
  Purchase #6 $174.33   4.721%   $182.5601   $182.56   $182.55   $182.60  
  Purchase #7 $157.59   3.205%   $162.6408   $162.64   $162.65   $162.60  
  7 purchase totals = $910.04       $976.5249   $976.53   $976.50   $976.50