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 $217.27   11.586%   $242.4429   $242.44   $242.45   $242.40  
  Purchase #2 $178.95   13.333%   $202.8094   $202.81   $202.80   $202.80  
  Purchase #3 $202.87   11.665%   $226.5348   $226.53   $226.55   $226.50  
  Purchase #4 $107.64   9.207%   $117.5504   $117.55   $117.55   $117.60  
  Purchase #5 $186.28   8.223%   $201.5978   $201.60   $201.60   $201.60  
  Purchase #6 $158.74   6.470%   $169.0105   $169.01   $169.00   $169.00  
  Purchase #7 $14.80   8.584%   $16.0704   $16.07   $16.05   $16.10  
  7 purchase totals = $1,066.55       $1,176.0162   $1,176.01   $1,176.00   $1,176.00