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 $14.49   13.464%   $16.4409   $16.44   $16.45   $16.40  
  Purchase #2 $167.71   9.135%   $183.0303   $183.03   $183.05   $183.00  
  Purchase #3 $217.52   7.828%   $234.5475   $234.55   $234.55   $234.50  
  Purchase #4 $58.92   12.119%   $66.0605   $66.06   $66.05   $66.10  
  Purchase #5 $60.60   5.477%   $63.9191   $63.92   $63.90   $63.90  
  Purchase #6 $219.92   9.203%   $240.1592   $240.16   $240.15   $240.20  
  Purchase #7 $158.54   8.187%   $171.5197   $171.52   $171.50   $171.50  
  7 purchase totals = $897.70       $975.6772   $975.68   $975.65   $975.60