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	$206.90	9.820%	$227.2176	$227.22	$227.20	$227.20
Purchase #2	$93.28	5.624%	$98.5261	$98.53	$98.55	$98.50
Purchase #3	$95.69	4.262%	$99.7683	$99.77	$99.75	$99.80
Purchase #4	$208.41	6.442%	$221.8358	$221.84	$221.85	$221.80
Purchase #5	$169.46	9.237%	$185.113	$185.11	$185.10	$185.10
Purchase #6	$220.48	13.608%	$250.4829	$250.48	$250.50	$250.50
Purchase #7	$196.53	5.483%	$207.3057	$207.31	$207.30	$207.30
7 purchase totals =	$1,190.75		$1,290.2494	$1,290.26	$1,290.25	$1,290.20