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 $22.44   9.674%   $24.6108   $24.61   $24.60   $24.60  
  Purchase #2 $126.72   11.415%   $141.1851   $141.19   $141.20   $141.20  
  Purchase #3 $161.95   7.426%   $173.9764   $173.98   $174.00   $174.00  
  Purchase #4 $201.87   4.422%   $210.7967   $210.80   $210.80   $210.80  
  Purchase #5 $159.42   12.828%   $179.8704   $179.87   $179.85   $179.90  
  Purchase #6 $60.31   6.630%   $64.3086   $64.31   $64.30   $64.30  
  Purchase #7 $114.34   8.804%   $124.4065   $124.41   $124.40   $124.40  
  7 purchase totals = $847.05       $919.1545   $919.17   $919.15   $919.20