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 $238.94   11.806%   $267.1493   $267.15   $267.15   $267.10  
  Purchase #2 $171.37   11.462%   $191.0124   $191.01   $191.00   $191.00  
  Purchase #3 $76.62   12.691%   $86.3438   $86.34   $86.35   $86.30  
  Purchase #4 $161.44   5.273%   $169.9527   $169.95   $169.95   $170.00  
  Purchase #5 $192.77   12.313%   $216.5058   $216.51   $216.50   $216.50  
  Purchase #6 $27.69   11.673%   $30.9223   $30.92   $30.90   $30.90  
  Purchase #7 $97.98   8.753%   $106.5562   $106.56   $106.55   $106.60  
  7 purchase totals = $966.81       $1,068.4425   $1,068.44   $1,068.40   $1,068.40