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 $62.73   10.416%   $69.264   $69.26   $69.25   $69.30  
  Purchase #2 $250.35   5.590%   $264.3446   $264.34   $264.35   $264.30  
  Purchase #3 $186.25   11.682%   $208.0077   $208.01   $208.00   $208.00  
  Purchase #4 $186.41   13.103%   $210.8353   $210.84   $210.85   $210.80  
  Purchase #5 $12.72   3.623%   $13.1808   $13.18   $13.20   $13.20  
  Purchase #6 $65.61   12.205%   $73.6177   $73.62   $73.60   $73.60  
  Purchase #7 $232.39   12.213%   $260.7718   $260.77   $260.75   $260.80  
  7 purchase totals = $996.46       $1,100.0219   $1,100.02   $1,100.00   $1,100.00