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 $108.83   3.223%   $112.3376   $112.34   $112.35   $112.30  
  Purchase #2 $96.66   11.287%   $107.57   $107.57   $107.55   $107.60  
  Purchase #3 $106.50   13.151%   $120.5058   $120.51   $120.50   $120.50  
  Purchase #4 $44.33   11.524%   $49.4386   $49.44   $49.45   $49.40  
  Purchase #5 $154.76   8.745%   $168.2938   $168.29   $168.30   $168.30  
  Purchase #6 $56.51   10.476%   $62.43   $62.43   $62.45   $62.40  
  Purchase #7 $126.69   6.536%   $134.9705   $134.97   $134.95   $135.00  
  7 purchase totals = $694.28       $755.5463   $755.55   $755.55   $755.50