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 $241.80   11.203%   $268.8889   $268.89   $268.90   $268.90  
  Purchase #2 $215.73   4.812%   $226.1109   $226.11   $226.10   $226.10  
  Purchase #3 $103.70   9.560%   $113.6137   $113.61   $113.60   $113.60  
  Purchase #4 $23.28   5.215%   $24.4941   $24.49   $24.50   $24.50  
  Purchase #5 $203.28   8.613%   $220.7885   $220.79   $220.80   $220.80  
  Purchase #6 $107.94   5.335%   $113.6986   $113.70   $113.70   $113.70  
  Purchase #7 $80.34   3.181%   $82.8956   $82.90   $82.90   $82.90  
  7 purchase totals = $976.07       $1,050.4903   $1,050.49   $1,050.50   $1,050.50