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	$71.36	13.608%	$81.0707	$81.07	$81.05	$81.10
Purchase #2	$19.77	4.192%	$20.5988	$20.60	$20.60	$20.60
Purchase #3	$186.69	9.496%	$204.4181	$204.42	$204.40	$204.40
Purchase #4	$55.48	7.666%	$59.7331	$59.73	$59.75	$59.70
Purchase #5	$35.36	4.790%	$37.0537	$37.05	$37.05	$37.10
Purchase #6	$77.67	11.587%	$86.6696	$86.67	$86.65	$86.70
Purchase #7	$37.96	6.583%	$40.4589	$40.46	$40.45	$40.50
7 purchase totals =	$484.29		$530.0029	$530.00	$529.95	$530.10