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 $249.47   10.594%   $275.8989   $275.90   $275.90   $275.90  
  Purchase #2 $88.86   5.697%   $93.9224   $93.92   $93.90   $93.90  
  Purchase #3 $129.27   12.857%   $145.8902   $145.89   $145.90   $145.90  
  Purchase #4 $94.98   3.843%   $98.6301   $98.63   $98.65   $98.60  
  Purchase #5 $217.31   6.539%   $231.5199   $231.52   $231.50   $231.50  
  Purchase #6 $12.75   12.324%   $14.3213   $14.32   $14.30   $14.30  
  Purchase #7 $61.55   4.415%   $64.2674   $64.27   $64.25   $64.30  
  7 purchase totals = $854.19       $924.4502   $924.45   $924.40   $924.40