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 $205.55   11.149%   $228.4668   $228.47   $228.45   $228.50  
  Purchase #2 $98.50   8.823%   $107.1907   $107.19   $107.20   $107.20  
  Purchase #3 $41.67   7.154%   $44.6511   $44.65   $44.65   $44.70  
  Purchase #4 $11.61   8.421%   $12.5877   $12.59   $12.60   $12.60  
  Purchase #5 $147.68   6.388%   $157.1138   $157.11   $157.10   $157.10  
  Purchase #6 $176.34   9.218%   $192.595   $192.60   $192.60   $192.60  
  Purchase #7 $67.33   6.785%   $71.8983   $71.90   $71.90   $71.90  
  7 purchase totals = $748.68       $814.5034   $814.51   $814.50   $814.60