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 $129.70   11.348%   $144.4184   $144.42   $144.40   $144.40  
  Purchase #2 $117.85   8.427%   $127.7812   $127.78   $127.80   $127.80  
  Purchase #3 $53.33   4.477%   $55.7176   $55.72   $55.70   $55.70  
  Purchase #4 $15.68   5.661%   $16.5676   $16.57   $16.55   $16.60  
  Purchase #5 $101.44   7.645%   $109.1951   $109.20   $109.20   $109.20  
  Purchase #6 $176.50   9.417%   $193.121   $193.12   $193.10   $193.10  
  Purchase #7 $197.94   12.860%   $223.3951   $223.40   $223.40   $223.40  
  7 purchase totals = $792.44       $870.1960   $870.21   $870.15   $870.20