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 $242.43   13.281%   $274.6271   $274.63   $274.65   $274.60  
  Purchase #2 $33.67   5.649%   $35.572   $35.57   $35.55   $35.60  
  Purchase #3 $36.72   9.627%   $40.255   $40.26   $40.25   $40.30  
  Purchase #4 $242.75   8.599%   $263.6241   $263.62   $263.60   $263.60  
  Purchase #5 $67.75   13.763%   $77.0744   $77.07   $77.05   $77.10  
  Purchase #6 $136.37   13.695%   $155.0459   $155.05   $155.05   $155.00  
  Purchase #7 $163.75   4.462%   $171.0565   $171.06   $171.05   $171.10  
  7 purchase totals = $923.44       $1,017.2550   $1,017.26   $1,017.20   $1,017.30