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	$147.74	13.654%	$167.9124	$167.91	$167.90	$167.90
Purchase #2	$85.98	12.581%	$96.7971	$96.80	$96.80	$96.80
Purchase #3	$126.90	13.309%	$143.7891	$143.79	$143.80	$143.80
Purchase #4	$158.50	8.860%	$172.5431	$172.54	$172.55	$172.50
Purchase #5	$239.92	4.349%	$250.3541	$250.35	$250.35	$250.40
Purchase #6	$170.36	5.503%	$179.7349	$179.73	$179.75	$179.70
Purchase #7	$66.56	4.104%	$69.2916	$69.29	$69.30	$69.30
7 purchase totals =	$995.96		$1,080.4223	$1,080.41	$1,080.45	$1,080.40