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 $213.58   8.110%   $230.9013   $230.90   $230.90   $230.90  
  Purchase #2 $177.68   13.478%   $201.6277   $201.63   $201.65   $201.60  
  Purchase #3 $204.42   5.767%   $216.2089   $216.21   $216.20   $216.20  
  Purchase #4 $216.62   8.313%   $234.6276   $234.63   $234.65   $234.60  
  Purchase #5 $48.74   4.386%   $50.8777   $50.88   $50.90   $50.90  
  Purchase #6 $231.86   4.477%   $242.2404   $242.24   $242.25   $242.20  
  Purchase #7 $46.75   8.273%   $50.6176   $50.62   $50.60   $50.60  
  7 purchase totals = $1,139.65       $1,227.1012   $1,227.11   $1,227.15   $1,227.00