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 $61.47   6.871%   $65.6936   $65.69   $65.70   $65.70  
  Purchase #2 $238.54   8.582%   $259.0115   $259.01   $259.00   $259.00  
  Purchase #3 $25.54   10.600%   $28.2472   $28.25   $28.25   $28.20  
  Purchase #4 $56.65   9.664%   $62.1247   $62.12   $62.10   $62.10  
  Purchase #5 $24.84   11.159%   $27.6119   $27.61   $27.60   $27.60  
  Purchase #6 $185.70   6.622%   $197.9971   $198.00   $198.00   $198.00  
  Purchase #7 $193.63   9.663%   $212.3405   $212.34   $212.35   $212.30  
  7 purchase totals = $786.37       $853.0265   $853.02   $853.00   $852.90