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 $10.57   6.239%   $11.2295   $11.23   $11.25   $11.20  
  Purchase #2 $122.69   9.377%   $134.1946   $134.19   $134.20   $134.20  
  Purchase #3 $60.64   6.381%   $64.5094   $64.51   $64.50   $64.50  
  Purchase #4 $149.72   13.484%   $169.9082   $169.91   $169.90   $169.90  
  Purchase #5 $244.85   6.833%   $261.5806   $261.58   $261.60   $261.60  
  Purchase #6 $240.44   13.381%   $272.6133   $272.61   $272.60   $272.60  
  Purchase #7 $163.84   6.380%   $174.293   $174.29   $174.30   $174.30  
  7 purchase totals = $992.75       $1,088.3286   $1,088.32   $1,088.35   $1,088.30