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 $167.58   4.442%   $175.0239   $175.02   $175.00   $175.00  
  Purchase #2 $140.75   6.502%   $149.9016   $149.90   $149.90   $149.90  
  Purchase #3 $20.96   12.566%   $23.5938   $23.59   $23.60   $23.60  
  Purchase #4 $206.45   10.238%   $227.5864   $227.59   $227.60   $227.60  
  Purchase #5 $187.91   6.254%   $199.6619   $199.66   $199.65   $199.70  
  Purchase #6 $211.85   11.638%   $236.5051   $236.51   $236.50   $236.50  
  Purchase #7 $237.81   7.247%   $255.0441   $255.04   $255.05   $255.00  
  7 purchase totals = $1,173.31       $1,267.3168   $1,267.31   $1,267.30   $1,267.30