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 $39.37   10.627%   $43.5538   $43.55   $43.55   $43.60  
  Purchase #2 $61.95   4.867%   $64.9651   $64.97   $64.95   $65.00  
  Purchase #3 $224.97   6.259%   $239.0509   $239.05   $239.05   $239.10  
  Purchase #4 $178.32   6.209%   $189.3919   $189.39   $189.40   $189.40  
  Purchase #5 $148.41   7.696%   $159.8316   $159.83   $159.85   $159.80  
  Purchase #6 $69.67   5.819%   $73.7241   $73.72   $73.70   $73.70  
  Purchase #7 $224.55   5.468%   $236.8284   $236.83   $236.85   $236.80  
  7 purchase totals = $947.24       $1,007.3458   $1,007.34   $1,007.35   $1,007.40