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 $69.56   7.505%   $74.7805   $74.78   $74.80   $74.80  
  Purchase #2 $179.94   7.648%   $193.7018   $193.70   $193.70   $193.70  
  Purchase #3 $156.88   5.176%   $165.0001   $165.00   $165.00   $165.00  
  Purchase #4 $107.59   10.845%   $119.2581   $119.26   $119.25   $119.30  
  Purchase #5 $93.63   13.430%   $106.2045   $106.20   $106.20   $106.20  
  Purchase #6 $185.71   5.178%   $195.3261   $195.33   $195.35   $195.30  
  Purchase #7 $10.45   11.109%   $11.6109   $11.61   $11.60   $11.60  
  7 purchase totals = $803.76       $865.8820   $865.88   $865.90   $865.90