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 $234.55   12.659%   $264.2417   $264.24   $264.25   $264.20  
  Purchase #2 $203.92   6.395%   $216.9607   $216.96   $216.95   $217.00  
  Purchase #3 $174.41   10.567%   $192.8399   $192.84   $192.85   $192.80  
  Purchase #4 $248.62   9.367%   $271.9082   $271.91   $271.90   $271.90  
  Purchase #5 $118.94   5.684%   $125.7005   $125.70   $125.70   $125.70  
  Purchase #6 $152.36   13.338%   $172.6818   $172.68   $172.70   $172.70  
  Purchase #7 $159.34   3.250%   $164.5186   $164.52   $164.50   $164.50  
  7 purchase totals = $1,292.14       $1,408.8514   $1,408.85   $1,408.85   $1,408.80