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 $233.45   3.777%   $242.2674   $242.27   $242.25   $242.30  
  Purchase #2 $80.73   13.446%   $91.585   $91.59   $91.60   $91.60  
  Purchase #3 $137.37   3.439%   $142.0942   $142.09   $142.10   $142.10  
  Purchase #4 $74.70   9.357%   $81.6897   $81.69   $81.70   $81.70  
  Purchase #5 $187.53   9.453%   $205.2572   $205.26   $205.25   $205.30  
  Purchase #6 $60.72   6.595%   $64.7245   $64.72   $64.70   $64.70  
  Purchase #7 $220.52   8.660%   $239.617   $239.62   $239.60   $239.60  
  7 purchase totals = $995.02       $1,067.2350   $1,067.24   $1,067.20   $1,067.30