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 $217.82   9.514%   $238.5434   $238.54   $238.55   $238.50  
  Purchase #2 $187.46   5.304%   $197.4029   $197.40   $197.40   $197.40  
  Purchase #3 $150.57   12.330%   $169.1353   $169.14   $169.15   $169.10  
  Purchase #4 $156.53   5.530%   $165.1861   $165.19   $165.20   $165.20  
  Purchase #5 $166.61   13.124%   $188.4759   $188.48   $188.50   $188.50  
  Purchase #6 $60.74   7.686%   $65.4085   $65.41   $65.40   $65.40  
  Purchase #7 $218.59   9.618%   $239.614   $239.61   $239.60   $239.60  
  7 purchase totals = $1,158.32       $1,263.7661   $1,263.77   $1,263.80   $1,263.70