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	$158.46	6.337%	$168.5016	$168.50	$168.50	$168.50
Purchase #2	$174.61	12.459%	$196.3647	$196.36	$196.35	$196.40
Purchase #3	$245.64	13.226%	$278.1283	$278.13	$278.15	$278.10
Purchase #4	$25.25	9.868%	$27.7417	$27.74	$27.75	$27.70
Purchase #5	$23.51	11.846%	$26.295	$26.30	$26.30	$26.30
Purchase #6	$54.72	13.872%	$62.3108	$62.31	$62.30	$62.30
Purchase #7	$91.46	4.171%	$95.2748	$95.27	$95.25	$95.30
7 purchase totals =	$773.65		$854.6169	$854.61	$854.60	$854.60