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 $239.97   12.361%   $269.6327   $269.63   $269.65   $269.60  
  Purchase #2 $32.61   13.748%   $37.0932   $37.09   $37.10   $37.10  
  Purchase #3 $92.27   6.242%   $98.0295   $98.03   $98.05   $98.00  
  Purchase #4 $110.96   7.382%   $119.1511   $119.15   $119.15   $119.20  
  Purchase #5 $205.94   8.310%   $223.0536   $223.05   $223.05   $223.10  
  Purchase #6 $76.98   6.622%   $82.0776   $82.08   $82.10   $82.10  
  Purchase #7 $120.83   11.596%   $134.8414   $134.84   $134.85   $134.80  
  7 purchase totals = $879.56       $963.8791   $963.87   $963.95   $963.90