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 $58.78   13.273%   $66.5819   $66.58   $66.60   $66.60  
  Purchase #2 $124.74   10.835%   $138.2556   $138.26   $138.25   $138.30  
  Purchase #3 $116.92   9.562%   $128.0999   $128.10   $128.10   $128.10  
  Purchase #4 $169.66   13.154%   $191.9771   $191.98   $192.00   $192.00  
  Purchase #5 $191.81   11.357%   $213.5939   $213.59   $213.60   $213.60  
  Purchase #6 $110.25   4.273%   $114.961   $114.96   $114.95   $115.00  
  Purchase #7 $165.27   10.380%   $182.425   $182.43   $182.45   $182.40  
  7 purchase totals = $937.43       $1,035.8944   $1,035.90   $1,035.95   $1,036.00