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 $53.95   13.687%   $61.3341   $61.33   $61.35   $61.30  
  Purchase #2 $227.84   3.699%   $236.2678   $236.27   $236.25   $236.30  
  Purchase #3 $84.35   11.339%   $93.9144   $93.91   $93.90   $93.90  
  Purchase #4 $53.52   8.333%   $57.9798   $57.98   $58.00   $58.00  
  Purchase #5 $110.77   8.804%   $120.5222   $120.52   $120.50   $120.50  
  Purchase #6 $170.51   7.866%   $183.9223   $183.92   $183.90   $183.90  
  Purchase #7 $20.82   10.269%   $22.958   $22.96   $22.95   $23.00  
  7 purchase totals = $721.76       $776.8986   $776.89   $776.85   $776.90