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 $169.41   7.522%   $182.153   $182.15   $182.15   $182.20  
  Purchase #2 $59.85   6.232%   $63.5799   $63.58   $63.60   $63.60  
  Purchase #3 $228.63   5.216%   $240.5553   $240.56   $240.55   $240.60  
  Purchase #4 $187.92   9.670%   $206.0919   $206.09   $206.10   $206.10  
  Purchase #5 $120.71   12.634%   $135.9605   $135.96   $135.95   $136.00  
  Purchase #6 $53.63   3.592%   $55.5564   $55.56   $55.55   $55.60  
  Purchase #7 $137.47   12.471%   $154.6139   $154.61   $154.60   $154.60  
  7 purchase totals = $957.62       $1,038.5109   $1,038.51   $1,038.50   $1,038.70