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 $44.64   9.299%   $48.7911   $48.79   $48.80   $48.80  
  Purchase #2 $175.64   4.720%   $183.9302   $183.93   $183.95   $183.90  
  Purchase #3 $128.56   12.185%   $144.225   $144.23   $144.25   $144.20  
  Purchase #4 $104.85   8.495%   $113.757   $113.76   $113.75   $113.80  
  Purchase #5 $65.47   12.560%   $73.693   $73.69   $73.70   $73.70  
  Purchase #6 $56.82   6.724%   $60.6406   $60.64   $60.65   $60.60  
  Purchase #7 $232.31   5.114%   $244.1903   $244.19   $244.20   $244.20  
  7 purchase totals = $808.29       $869.2272   $869.23   $869.30   $869.20