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 $62.80   10.574%   $69.4405   $69.44   $69.45   $69.40  
  Purchase #2 $196.53   9.356%   $214.9173   $214.92   $214.90   $214.90  
  Purchase #3 $242.84   11.837%   $271.585   $271.59   $271.60   $271.60  
  Purchase #4 $16.86   4.295%   $17.5841   $17.58   $17.60   $17.60  
  Purchase #5 $146.51   11.229%   $162.9616   $162.96   $162.95   $163.00  
  Purchase #6 $99.27   11.788%   $110.9719   $110.97   $110.95   $111.00  
  Purchase #7 $204.95   10.744%   $226.9698   $226.97   $226.95   $227.00  
  7 purchase totals = $969.76       $1,074.4302   $1,074.43   $1,074.40   $1,074.50