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 $90.67   13.821%   $103.2015   $103.20   $103.20   $103.20  
  Purchase #2 $225.88   7.428%   $242.6584   $242.66   $242.65   $242.70  
  Purchase #3 $174.32   5.605%   $184.0906   $184.09   $184.10   $184.10  
  Purchase #4 $156.55   9.483%   $171.3956   $171.40   $171.40   $171.40  
  Purchase #5 $124.76   10.296%   $137.6053   $137.61   $137.60   $137.60  
  Purchase #6 $212.65   10.205%   $234.3509   $234.35   $234.35   $234.40  
  Purchase #7 $80.68   4.151%   $84.029   $84.03   $84.05   $84.00  
  7 purchase totals = $1,065.51       $1,157.3313   $1,157.34   $1,157.35   $1,157.40