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 $144.65   11.116%   $160.7293   $160.73   $160.75   $160.70  
  Purchase #2 $242.25   10.624%   $267.9866   $267.99   $268.00   $268.00  
  Purchase #3 $155.65   11.664%   $173.805   $173.81   $173.80   $173.80  
  Purchase #4 $79.39   13.798%   $90.3442   $90.34   $90.35   $90.30  
  Purchase #5 $119.80   8.527%   $130.0153   $130.02   $130.00   $130.00  
  Purchase #6 $97.63   10.336%   $107.721   $107.72   $107.70   $107.70  
  Purchase #7 $87.53   4.194%   $91.201   $91.20   $91.20   $91.20  
  7 purchase totals = $926.90       $1,021.8024   $1,021.81   $1,021.80   $1,021.70