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 $64.75   8.644%   $70.347   $70.35   $70.35   $70.30  
  Purchase #2 $204.53   4.766%   $214.2779   $214.28   $214.30   $214.30  
  Purchase #3 $43.80   10.306%   $48.314   $48.31   $48.30   $48.30  
  Purchase #4 $70.54   7.863%   $76.0866   $76.09   $76.10   $76.10  
  Purchase #5 $163.28   13.632%   $185.5383   $185.54   $185.55   $185.50  
  Purchase #6 $129.79   13.721%   $147.5985   $147.60   $147.60   $147.60  
  Purchase #7 $35.87   11.221%   $39.895   $39.90   $39.90   $39.90  
  7 purchase totals = $712.56       $782.0573   $782.07   $782.10   $782.00