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 $161.34   13.748%   $183.521   $183.52   $183.50   $183.50  
  Purchase #2 $31.33   11.176%   $34.8314   $34.83   $34.85   $34.80  
  Purchase #3 $184.53   3.290%   $190.601   $190.60   $190.60   $190.60  
  Purchase #4 $140.54   5.784%   $148.6688   $148.67   $148.65   $148.70  
  Purchase #5 $114.50   5.324%   $120.596   $120.60   $120.60   $120.60  
  Purchase #6 $171.92   13.543%   $195.2031   $195.20   $195.20   $195.20  
  Purchase #7 $139.97   7.352%   $150.2606   $150.26   $150.25   $150.30  
  7 purchase totals = $944.13       $1,023.6819   $1,023.68   $1,023.65   $1,023.70