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 $54.36   11.458%   $60.5886   $60.59   $60.60   $60.60  
  Purchase #2 $227.73   12.863%   $257.0229   $257.02   $257.00   $257.00  
  Purchase #3 $182.89   6.802%   $195.3302   $195.33   $195.35   $195.30  
  Purchase #4 $233.77   6.304%   $248.5069   $248.51   $248.50   $248.50  
  Purchase #5 $144.96   11.367%   $161.4376   $161.44   $161.45   $161.40  
  Purchase #6 $53.44   13.550%   $60.6811   $60.68   $60.70   $60.70  
  Purchase #7 $112.45   10.326%   $124.0616   $124.06   $124.05   $124.10  
  7 purchase totals = $1,009.60       $1,107.6289   $1,107.63   $1,107.65   $1,107.60