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 $53.83   8.185%   $58.236   $58.24   $58.25   $58.20  
  Purchase #2 $67.76   10.635%   $74.9663   $74.97   $74.95   $75.00  
  Purchase #3 $176.52   4.588%   $184.6187   $184.62   $184.60   $184.60  
  Purchase #4 $219.67   6.304%   $233.518   $233.52   $233.50   $233.50  
  Purchase #5 $174.51   5.213%   $183.6072   $183.61   $183.60   $183.60  
  Purchase #6 $139.28   9.352%   $152.3055   $152.31   $152.30   $152.30  
  Purchase #7 $63.82   10.185%   $70.3201   $70.32   $70.30   $70.30  
  7 purchase totals = $895.39       $957.5718   $957.59   $957.50   $957.50