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 $88.81   9.504%   $97.2505   $97.25   $97.25   $97.30  
  Purchase #2 $22.47   9.518%   $24.6087   $24.61   $24.60   $24.60  
  Purchase #3 $32.54   3.478%   $33.6717   $33.67   $33.65   $33.70  
  Purchase #4 $150.75   12.815%   $170.0686   $170.07   $170.05   $170.10  
  Purchase #5 $241.63   10.488%   $266.9722   $266.97   $266.95   $267.00  
  Purchase #6 $130.90   7.256%   $140.3981   $140.40   $140.40   $140.40  
  Purchase #7 $9.65   9.350%   $10.5523   $10.55   $10.55   $10.60  
  7 purchase totals = $676.75       $743.5221   $743.52   $743.45   $743.70