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	$161.43	12.682%	$181.9026	$181.90	$181.90	$181.90
Purchase #2	$51.53	4.126%	$53.6561	$53.66	$53.65	$53.70
Purchase #3	$93.36	7.726%	$100.573	$100.57	$100.55	$100.60
Purchase #4	$112.88	5.334%	$118.901	$118.90	$118.90	$118.90
Purchase #5	$39.56	13.836%	$45.0335	$45.03	$45.05	$45.00
Purchase #6	$44.60	11.281%	$49.6313	$49.63	$49.65	$49.60
Purchase #7	$88.29	11.874%	$98.7736	$98.77	$98.75	$98.80
7 purchase totals =	$591.65		$648.4711	$648.46	$648.45	$648.50