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 $124.28   13.548%   $141.1175   $141.12   $141.10   $141.10  
  Purchase #2 $190.54   5.278%   $200.5967   $200.60   $200.60   $200.60  
  Purchase #3 $137.42   7.669%   $147.9587   $147.96   $147.95   $148.00  
  Purchase #4 $107.36   13.194%   $121.5251   $121.53   $121.55   $121.50  
  Purchase #5 $208.99   8.350%   $226.4407   $226.44   $226.45   $226.40  
  Purchase #6 $97.90   11.429%   $109.089   $109.09   $109.10   $109.10  
  Purchase #7 $121.78   6.321%   $129.4777   $129.48   $129.50   $129.50  
  7 purchase totals = $988.27       $1,076.2054   $1,076.22   $1,076.25   $1,076.20