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 $48.67   9.231%   $53.1627   $53.16   $53.15   $53.20  
  Purchase #2 $48.63   4.202%   $50.6734   $50.67   $50.65   $50.70  
  Purchase #3 $55.37   4.429%   $57.8223   $57.82   $57.80   $57.80  
  Purchase #4 $222.86   12.867%   $251.5354   $251.54   $251.55   $251.50  
  Purchase #5 $215.80   8.850%   $234.8983   $234.90   $234.90   $234.90  
  Purchase #6 $209.93   11.693%   $234.4771   $234.48   $234.50   $234.50  
  Purchase #7 $58.40   3.222%   $60.2816   $60.28   $60.30   $60.30  
  7 purchase totals = $859.66       $942.8508   $942.85   $942.85   $942.90