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	$165.53	3.304%	$170.9991	$171.00	$171.00	$171.00
Purchase #2	$246.56	7.299%	$264.5564	$264.56	$264.55	$264.60
Purchase #3	$184.48	7.521%	$198.3547	$198.35	$198.35	$198.40
Purchase #4	$96.52	13.397%	$109.4508	$109.45	$109.45	$109.50
Purchase #5	$124.66	4.312%	$130.0353	$130.04	$130.05	$130.00
Purchase #6	$52.46	3.608%	$54.3528	$54.35	$54.35	$54.40
Purchase #7	$115.74	10.521%	$127.917	$127.92	$127.90	$127.90
7 purchase totals =	$985.95		$1,055.6661	$1,055.67	$1,055.65	$1,055.80