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 $150.28   11.647%   $167.7831   $167.78   $167.80   $167.80  
  Purchase #2 $244.63   12.517%   $275.2503   $275.25   $275.25   $275.30  
  Purchase #3 $238.48   4.801%   $249.9294   $249.93   $249.95   $249.90  
  Purchase #4 $240.78   13.523%   $273.3407   $273.34   $273.35   $273.30  
  Purchase #5 $182.81   5.282%   $192.466   $192.47   $192.45   $192.50  
  Purchase #6 $191.34   3.262%   $197.5815   $197.58   $197.60   $197.60  
  Purchase #7 $6.61   8.582%   $7.1773   $7.18   $7.20   $7.20  
  7 purchase totals = $1,254.93       $1,363.5283   $1,363.53   $1,363.60   $1,363.60