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 $85.25   8.621%   $92.5994   $92.60   $92.60   $92.60  
  Purchase #2 $135.40   10.550%   $149.6847   $149.68   $149.70   $149.70  
  Purchase #3 $118.96   10.420%   $131.3556   $131.36   $131.35   $131.40  
  Purchase #4 $104.91   12.484%   $118.007   $118.01   $118.00   $118.00  
  Purchase #5 $20.95   9.267%   $22.8914   $22.89   $22.90   $22.90  
  Purchase #6 $154.38   3.744%   $160.16   $160.16   $160.15   $160.20  
  Purchase #7 $93.95   7.833%   $101.3091   $101.31   $101.30   $101.30  
  7 purchase totals = $713.80       $776.0072   $776.01   $776.00   $776.10