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	$21.25	12.111%	$23.8236	$23.82	$23.80	$23.80
Purchase #2	$136.48	8.389%	$147.9293	$147.93	$147.95	$147.90
Purchase #3	$80.91	7.336%	$86.8456	$86.85	$86.85	$86.80
Purchase #4	$44.25	3.456%	$45.7793	$45.78	$45.80	$45.80
Purchase #5	$214.95	13.167%	$243.2525	$243.25	$243.25	$243.30
Purchase #6	$76.93	4.534%	$80.418	$80.42	$80.40	$80.40
Purchase #7	$215.87	3.662%	$223.7752	$223.78	$223.80	$223.80
7 purchase totals =	$790.64		$851.8235	$851.83	$851.85	$851.80