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 $208.65   13.828%   $237.5021   $237.50   $237.50   $237.50  
  Purchase #2 $150.26   3.657%   $155.755   $155.76   $155.75   $155.80  
  Purchase #3 $36.74   4.497%   $38.3922   $38.39   $38.40   $38.40  
  Purchase #4 $105.68   13.345%   $119.783   $119.78   $119.80   $119.80  
  Purchase #5 $160.75   8.634%   $174.6292   $174.63   $174.65   $174.60  
  Purchase #6 $112.43   4.676%   $117.6872   $117.69   $117.70   $117.70  
  Purchase #7 $210.99   4.378%   $220.2271   $220.23   $220.25   $220.20  
  7 purchase totals = $985.50       $1,063.9758   $1,063.98   $1,064.05   $1,064.00