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 $89.44   13.625%   $101.6262   $101.63   $101.65   $101.60  
  Purchase #2 $72.91   4.245%   $76.005   $76.01   $76.00   $76.00  
  Purchase #3 $35.78   4.341%   $37.3332   $37.33   $37.35   $37.30  
  Purchase #4 $179.74   8.297%   $194.653   $194.65   $194.65   $194.70  
  Purchase #5 $60.66   12.363%   $68.1594   $68.16   $68.15   $68.20  
  Purchase #6 $214.97   11.655%   $240.0248   $240.02   $240.00   $240.00  
  Purchase #7 $157.26   12.239%   $176.5071   $176.51   $176.50   $176.50  
  7 purchase totals = $810.76       $894.3087   $894.31   $894.30   $894.30