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 $246.78   6.137%   $261.9249   $261.92   $261.90   $261.90  
  Purchase #2 $42.35   13.427%   $48.0363   $48.04   $48.05   $48.00  
  Purchase #3 $44.64   5.721%   $47.1939   $47.19   $47.20   $47.20  
  Purchase #4 $177.40   5.473%   $187.1091   $187.11   $187.10   $187.10  
  Purchase #5 $74.33   12.465%   $83.5952   $83.60   $83.60   $83.60  
  Purchase #6 $241.89   5.682%   $255.6342   $255.63   $255.65   $255.60  
  Purchase #7 $85.31   9.490%   $93.4059   $93.41   $93.40   $93.40  
  7 purchase totals = $912.70       $976.8995   $976.90   $976.90   $976.80