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	$35.53	5.527%	$37.4937	$37.49	$37.50	$37.50
Purchase #2	$59.83	5.171%	$62.9238	$62.92	$62.90	$62.90
Purchase #3	$34.38	13.536%	$39.0337	$39.03	$39.05	$39.00
Purchase #4	$160.81	7.571%	$172.9849	$172.98	$173.00	$173.00
Purchase #5	$162.72	5.274%	$171.3019	$171.30	$171.30	$171.30
Purchase #6	$237.59	5.361%	$250.3272	$250.33	$250.35	$250.30
Purchase #7	$73.49	9.624%	$80.5627	$80.56	$80.55	$80.60
7 purchase totals =	$764.35		$814.6279	$814.61	$814.65	$814.60