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 $183.51   5.177%   $193.0103   $193.01   $193.00   $193.00  
  Purchase #2 $180.36   11.429%   $200.9733   $200.97   $200.95   $201.00  
  Purchase #3 $143.65   8.874%   $156.3975   $156.40   $156.40   $156.40  
  Purchase #4 $49.31   9.276%   $53.884   $53.88   $53.90   $53.90  
  Purchase #5 $51.57   7.162%   $55.2634   $55.26   $55.25   $55.30  
  Purchase #6 $26.59   12.273%   $29.8534   $29.85   $29.85   $29.90  
  Purchase #7 $9.57   10.812%   $10.6047   $10.60   $10.60   $10.60  
  7 purchase totals = $644.56       $699.9866   $699.97   $699.95   $700.10