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 $148.99   10.731%   $164.9781   $164.98   $165.00   $165.00  
  Purchase #2 $220.91   8.496%   $239.6785   $239.68   $239.70   $239.70  
  Purchase #3 $68.38   9.157%   $74.6416   $74.64   $74.65   $74.60  
  Purchase #4 $182.35   5.491%   $192.3628   $192.36   $192.35   $192.40  
  Purchase #5 $49.61   12.732%   $55.9263   $55.93   $55.95   $55.90  
  Purchase #6 $27.51   10.190%   $30.3133   $30.31   $30.30   $30.30  
  Purchase #7 $127.49   8.168%   $137.9034   $137.90   $137.90   $137.90  
  7 purchase totals = $825.24       $895.8040   $895.80   $895.85   $895.80