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 $139.57   10.117%   $153.6903   $153.69   $153.70   $153.70  
  Purchase #2 $146.26   11.378%   $162.9015   $162.90   $162.90   $162.90  
  Purchase #3 $111.58   11.394%   $124.2934   $124.29   $124.30   $124.30  
  Purchase #4 $43.50   13.858%   $49.5282   $49.53   $49.55   $49.50  
  Purchase #5 $116.80   6.255%   $124.1058   $124.11   $124.10   $124.10  
  Purchase #6 $48.96   5.633%   $51.7179   $51.72   $51.70   $51.70  
  Purchase #7 $132.70   13.869%   $151.1042   $151.10   $151.10   $151.10  
  7 purchase totals = $739.37       $817.3413   $817.34   $817.35   $817.30