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	$116.99	11.530%	$130.4789	$130.48	$130.50	$130.50
Purchase #2	$19.31	4.546%	$20.1878	$20.19	$20.20	$20.20
Purchase #3	$49.35	11.737%	$55.1422	$55.14	$55.15	$55.10
Purchase #4	$35.36	11.199%	$39.32	$39.32	$39.30	$39.30
Purchase #5	$198.77	12.326%	$223.2704	$223.27	$223.25	$223.30
Purchase #6	$150.38	12.525%	$169.2151	$169.22	$169.20	$169.20
Purchase #7	$31.25	3.728%	$32.415	$32.42	$32.40	$32.40
7 purchase totals =	$601.41		$670.0294	$670.04	$670.00	$670.00