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 $23.32   12.535%   $26.2432   $26.24   $26.25   $26.20  
  Purchase #2 $232.58   7.730%   $250.5584   $250.56   $250.55   $250.60  
  Purchase #3 $23.43   9.158%   $25.5757   $25.58   $25.60   $25.60  
  Purchase #4 $206.68   4.813%   $216.6275   $216.63   $216.65   $216.60  
  Purchase #5 $126.78   3.350%   $131.0271   $131.03   $131.05   $131.00  
  Purchase #6 $57.54   11.498%   $64.1559   $64.16   $64.15   $64.20  
  Purchase #7 $64.28   6.147%   $68.2313   $68.23   $68.25   $68.20  
  7 purchase totals = $734.61       $782.4191   $782.43   $782.50   $782.40