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 $52.58   5.466%   $55.454   $55.45   $55.45   $55.50  
  Purchase #2 $85.50   8.141%   $92.4606   $92.46   $92.45   $92.50  
  Purchase #3 $181.59   8.851%   $197.6625   $197.66   $197.65   $197.70  
  Purchase #4 $84.71   4.565%   $88.577   $88.58   $88.60   $88.60  
  Purchase #5 $103.90   11.632%   $115.9856   $115.99   $116.00   $116.00  
  Purchase #6 $36.97   3.507%   $38.2665   $38.27   $38.25   $38.30  
  Purchase #7 $129.27   11.847%   $144.5846   $144.58   $144.60   $144.60  
  7 purchase totals = $674.52       $732.9908   $732.99   $733.00   $733.20