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 $219.96   13.811%   $250.3387   $250.34   $250.35   $250.30  
  Purchase #2 $182.48   13.742%   $207.5564   $207.56   $207.55   $207.60  
  Purchase #3 $235.98   4.509%   $246.6203   $246.62   $246.60   $246.60  
  Purchase #4 $12.64   13.643%   $14.3645   $14.36   $14.35   $14.40  
  Purchase #5 $179.69   8.421%   $194.8217   $194.82   $194.80   $194.80  
  Purchase #6 $223.28   12.872%   $252.0206   $252.02   $252.00   $252.00  
  Purchase #7 $94.74   3.696%   $98.2416   $98.24   $98.25   $98.20  
  7 purchase totals = $1,148.77       $1,263.9638   $1,263.96   $1,263.90   $1,263.90