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 $146.99   12.620%   $165.5401   $165.54   $165.55   $165.50  
  Purchase #2 $229.37   7.481%   $246.5292   $246.53   $246.55   $246.50  
  Purchase #3 $118.59   12.684%   $133.632   $133.63   $133.65   $133.60  
  Purchase #4 $168.44   12.525%   $189.5371   $189.54   $189.55   $189.50  
  Purchase #5 $206.75   3.444%   $213.8705   $213.87   $213.85   $213.90  
  Purchase #6 $159.47   13.244%   $180.5902   $180.59   $180.60   $180.60  
  Purchase #7 $126.97   4.208%   $132.3129   $132.31   $132.30   $132.30  
  7 purchase totals = $1,156.58       $1,262.0120   $1,262.01   $1,262.05   $1,261.90