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 $61.39   12.137%   $68.8409   $68.84   $68.85   $68.80  
  Purchase #2 $245.64   10.303%   $270.9483   $270.95   $270.95   $270.90  
  Purchase #3 $186.85   4.211%   $194.7183   $194.72   $194.70   $194.70  
  Purchase #4 $49.28   5.134%   $51.81   $51.81   $51.80   $51.80  
  Purchase #5 $208.88   4.507%   $218.2942   $218.29   $218.30   $218.30  
  Purchase #6 $194.89   6.795%   $208.1328   $208.13   $208.15   $208.10  
  Purchase #7 $102.99   3.698%   $106.7986   $106.80   $106.80   $106.80  
  7 purchase totals = $1,049.92       $1,119.5431   $1,119.54   $1,119.55   $1,119.40