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	$40.64	11.648%	$45.3737	$45.37	$45.35	$45.40
Purchase #2	$40.87	12.865%	$46.1279	$46.13	$46.15	$46.10
Purchase #3	$179.66	11.695%	$200.6712	$200.67	$200.65	$200.70
Purchase #4	$73.99	9.594%	$81.0886	$81.09	$81.10	$81.10
Purchase #5	$43.52	7.469%	$46.7705	$46.77	$46.75	$46.80
Purchase #6	$129.91	9.813%	$142.6581	$142.66	$142.65	$142.70
Purchase #7	$76.91	11.233%	$85.5493	$85.55	$85.55	$85.50
7 purchase totals =	$585.50		$648.2393	$648.24	$648.20	$648.30