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 $61.27   12.570%   $68.9716   $68.97   $68.95   $69.00  
  Purchase #2 $215.27   13.763%   $244.8976   $244.90   $244.90   $244.90  
  Purchase #3 $77.92   4.440%   $81.3796   $81.38   $81.40   $81.40  
  Purchase #4 $200.40   9.743%   $219.925   $219.93   $219.95   $219.90  
  Purchase #5 $14.72   9.536%   $16.1237   $16.12   $16.10   $16.10  
  Purchase #6 $171.66   11.463%   $191.3374   $191.34   $191.35   $191.30  
  Purchase #7 $44.79   13.408%   $50.7954   $50.80   $50.80   $50.80  
  7 purchase totals = $786.03       $873.4303   $873.44   $873.45   $873.40