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 $118.97   6.598%   $126.8196   $126.82   $126.80   $126.80  
  Purchase #2 $143.75   6.193%   $152.6524   $152.65   $152.65   $152.70  
  Purchase #3 $35.97   4.385%   $37.5473   $37.55   $37.55   $37.50  
  Purchase #4 $204.54   8.240%   $221.3941   $221.39   $221.40   $221.40  
  Purchase #5 $137.33   11.235%   $152.759   $152.76   $152.75   $152.80  
  Purchase #6 $60.40   11.713%   $67.4747   $67.47   $67.45   $67.50  
  Purchase #7 $54.84   5.743%   $57.9895   $57.99   $58.00   $58.00  
  7 purchase totals = $755.80       $816.6366   $816.63   $816.60   $816.70