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 $43.36   7.472%   $46.5999   $46.60   $46.60   $46.60  
  Purchase #2 $169.92   12.781%   $191.6375   $191.64   $191.65   $191.60  
  Purchase #3 $157.31   3.717%   $163.1572   $163.16   $163.15   $163.20  
  Purchase #4 $89.33   5.672%   $94.3968   $94.40   $94.40   $94.40  
  Purchase #5 $212.98   13.105%   $240.891   $240.89   $240.90   $240.90  
  Purchase #6 $5.84   3.668%   $6.0542   $6.05   $6.05   $6.10  
  Purchase #7 $149.91   7.196%   $160.6975   $160.70   $160.70   $160.70  
  7 purchase totals = $828.65       $903.4341   $903.44   $903.45   $903.50