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	$81.82	11.438%	$91.1786	$91.18	$91.20	$91.20
Purchase #2	$37.87	12.804%	$42.7189	$42.72	$42.70	$42.70
Purchase #3	$53.95	10.293%	$59.5031	$59.50	$59.50	$59.50
Purchase #4	$97.69	3.758%	$101.3612	$101.36	$101.35	$101.40
Purchase #5	$107.50	9.534%	$117.7491	$117.75	$117.75	$117.70
Purchase #6	$75.27	13.445%	$85.3901	$85.39	$85.40	$85.40
Purchase #7	$38.63	10.403%	$42.6487	$42.65	$42.65	$42.60
7 purchase totals =	$492.73		$540.5497	$540.55	$540.55	$540.50