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	$15.78	4.674%	$16.5176	$16.52	$16.50	$16.50
Purchase #2	$207.33	12.657%	$233.5718	$233.57	$233.55	$233.60
Purchase #3	$32.50	10.431%	$35.8901	$35.89	$35.90	$35.90
Purchase #4	$119.67	6.252%	$127.1518	$127.15	$127.15	$127.20
Purchase #5	$20.63	10.442%	$22.7842	$22.78	$22.80	$22.80
Purchase #6	$181.63	11.275%	$202.1088	$202.11	$202.10	$202.10
Purchase #7	$182.85	7.488%	$196.5418	$196.54	$196.55	$196.50
7 purchase totals =	$760.39		$834.5661	$834.56	$834.55	$834.60