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 $163.99   10.503%   $181.2139   $181.21   $181.20   $181.20  
  Purchase #2 $180.68   9.263%   $197.4164   $197.42   $197.40   $197.40  
  Purchase #3 $201.92   11.389%   $224.9167   $224.92   $224.90   $224.90  
  Purchase #4 $49.66   9.348%   $54.3022   $54.30   $54.30   $54.30  
  Purchase #5 $109.62   12.567%   $123.3959   $123.40   $123.40   $123.40  
  Purchase #6 $68.90   6.674%   $73.4984   $73.50   $73.50   $73.50  
  Purchase #7 $214.28   13.278%   $242.7321   $242.73   $242.75   $242.70  
  7 purchase totals = $989.05       $1,097.4756   $1,097.48   $1,097.45   $1,097.40