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 $14.65   10.141%   $16.1357   $16.14   $16.15   $16.10  
  Purchase #2 $161.73   8.155%   $174.9191   $174.92   $174.90   $174.90  
  Purchase #3 $152.55   12.164%   $171.1062   $171.11   $171.10   $171.10  
  Purchase #4 $163.82   4.716%   $171.5458   $171.55   $171.55   $171.50  
  Purchase #5 $24.72   3.608%   $25.6119   $25.61   $25.60   $25.60  
  Purchase #6 $137.72   7.429%   $147.9512   $147.95   $147.95   $148.00  
  Purchase #7 $50.36   8.391%   $54.5857   $54.59   $54.60   $54.60  
  7 purchase totals = $705.55       $761.8556   $761.87   $761.85   $761.80