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	$129.67	12.732%	$146.1796	$146.18	$146.20	$146.20
Purchase #2	$235.90	12.218%	$264.7223	$264.72	$264.70	$264.70
Purchase #3	$191.89	9.529%	$210.1752	$210.18	$210.20	$210.20
Purchase #4	$207.88	10.180%	$229.0422	$229.04	$229.05	$229.00
Purchase #5	$32.42	9.358%	$35.4539	$35.45	$35.45	$35.50
Purchase #6	$131.74	12.751%	$148.5382	$148.54	$148.55	$148.50
Purchase #7	$66.54	8.657%	$72.3004	$72.30	$72.30	$72.30
7 purchase totals =	$996.04		$1,106.4118	$1,106.41	$1,106.45	$1,106.40