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	$162.73	11.173%	$180.9118	$180.91	$180.90	$180.90
Purchase #2	$210.33	7.349%	$225.7872	$225.79	$225.80	$225.80
Purchase #3	$143.57	7.163%	$153.8539	$153.85	$153.85	$153.90
Purchase #4	$80.73	12.314%	$90.6711	$90.67	$90.65	$90.70
Purchase #5	$229.26	5.741%	$242.4218	$242.42	$242.40	$242.40
Purchase #6	$242.96	12.748%	$273.9325	$273.93	$273.95	$273.90
Purchase #7	$207.92	7.600%	$223.7219	$223.72	$223.70	$223.70
7 purchase totals =	$1,277.50		$1,391.3002	$1,391.29	$1,391.25	$1,391.30