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 $46.37   12.805%   $52.3077   $52.31   $52.30   $52.30  
  Purchase #2 $194.43   3.390%   $201.0212   $201.02   $201.00   $201.00  
  Purchase #3 $248.73   8.364%   $269.5338   $269.53   $269.55   $269.50  
  Purchase #4 $247.70   4.729%   $259.4137   $259.41   $259.40   $259.40  
  Purchase #5 $209.65   12.617%   $236.1015   $236.10   $236.10   $236.10  
  Purchase #6 $193.42   10.470%   $213.6711   $213.67   $213.65   $213.70  
  Purchase #7 $244.61   9.172%   $267.0456   $267.05   $267.05   $267.00  
  7 purchase totals = $1,384.91       $1,499.0946   $1,499.09   $1,499.05   $1,499.00