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 $164.69   13.622%   $187.1241   $187.12   $187.10   $187.10  
  Purchase #2 $241.95   11.521%   $269.8251   $269.83   $269.85   $269.80  
  Purchase #3 $85.25   8.607%   $92.5875   $92.59   $92.60   $92.60  
  Purchase #4 $7.87   9.694%   $8.6329   $8.63   $8.65   $8.60  
  Purchase #5 $241.78   5.322%   $254.6475   $254.65   $254.65   $254.60  
  Purchase #6 $207.56   8.133%   $224.4409   $224.44   $224.45   $224.40  
  Purchase #7 $16.31   6.827%   $17.4235   $17.42   $17.40   $17.40  
  7 purchase totals = $965.41       $1,054.6815   $1,054.68   $1,054.70   $1,054.50