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 $170.83   3.308%   $176.4811   $176.48   $176.50   $176.50  
  Purchase #2 $101.90   4.103%   $106.081   $106.08   $106.10   $106.10  
  Purchase #3 $173.52   6.683%   $185.1163   $185.12   $185.10   $185.10  
  Purchase #4 $35.87   10.243%   $39.5442   $39.54   $39.55   $39.50  
  Purchase #5 $36.62   8.860%   $39.8645   $39.86   $39.85   $39.90  
  Purchase #6 $19.88   11.844%   $22.2346   $22.23   $22.25   $22.20  
  Purchase #7 $17.79   3.583%   $18.4274   $18.43   $18.45   $18.40  
  7 purchase totals = $556.41       $587.7491   $587.74   $587.80   $587.70