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 $198.38   10.715%   $219.6364   $219.64   $219.65   $219.60  
  Purchase #2 $245.35   6.766%   $261.9504   $261.95   $261.95   $262.00  
  Purchase #3 $67.44   6.464%   $71.7993   $71.80   $71.80   $71.80  
  Purchase #4 $103.65   8.546%   $112.5079   $112.51   $112.50   $112.50  
  Purchase #5 $123.89   9.156%   $135.2334   $135.23   $135.25   $135.20  
  Purchase #6 $74.84   6.393%   $79.6245   $79.62   $79.60   $79.60  
  Purchase #7 $151.64   13.176%   $171.6201   $171.62   $171.60   $171.60  
  7 purchase totals = $965.19       $1,052.3720   $1,052.37   $1,052.35   $1,052.30