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 $228.78   11.534%   $255.1675   $255.17   $255.15   $255.20  
  Purchase #2 $191.28   6.485%   $203.6845   $203.68   $203.70   $203.70  
  Purchase #3 $18.25   4.490%   $19.0694   $19.07   $19.05   $19.10  
  Purchase #4 $56.34   12.500%   $63.3825   $63.38   $63.40   $63.40  
  Purchase #5 $223.65   8.515%   $242.6938   $242.69   $242.70   $242.70  
  Purchase #6 $218.36   10.459%   $241.1983   $241.20   $241.20   $241.20  
  Purchase #7 $168.69   4.333%   $175.9993   $176.00   $176.00   $176.00  
  7 purchase totals = $1,105.35       $1,201.1953   $1,201.19   $1,201.20   $1,201.30