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 $224.91   9.689%   $246.7015   $246.70   $246.70   $246.70  
  Purchase #2 $150.88   5.679%   $159.4485   $159.45   $159.45   $159.40  
  Purchase #3 $207.64   4.305%   $216.5789   $216.58   $216.60   $216.60  
  Purchase #4 $71.34   10.729%   $78.9941   $78.99   $79.00   $79.00  
  Purchase #5 $66.31   10.480%   $73.2593   $73.26   $73.25   $73.30  
  Purchase #6 $84.44   9.723%   $92.6501   $92.65   $92.65   $92.70  
  Purchase #7 $188.69   3.300%   $194.9168   $194.92   $194.90   $194.90  
  7 purchase totals = $994.21       $1,062.5492   $1,062.55   $1,062.55   $1,062.60