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 $111.50   12.771%   $125.7397   $125.74   $125.75   $125.70  
  Purchase #2 $23.88   10.856%   $26.4724   $26.47   $26.45   $26.50  
  Purchase #3 $84.54   3.140%   $87.1946   $87.19   $87.20   $87.20  
  Purchase #4 $241.71   6.485%   $257.3849   $257.38   $257.40   $257.40  
  Purchase #5 $141.51   6.699%   $150.9898   $150.99   $151.00   $151.00  
  Purchase #6 $173.81   10.798%   $192.578   $192.58   $192.60   $192.60  
  Purchase #7 $25.54   3.568%   $26.4513   $26.45   $26.45   $26.50  
  7 purchase totals = $802.49       $866.8107   $866.80   $866.85   $866.90