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	$109.82	10.838%	$121.7223	$121.72	$121.70	$121.70
Purchase #2	$39.71	11.107%	$44.1206	$44.12	$44.10	$44.10
Purchase #3	$83.64	8.747%	$90.956	$90.96	$90.95	$91.00
Purchase #4	$173.64	6.766%	$185.3885	$185.39	$185.40	$185.40
Purchase #5	$18.46	7.392%	$19.8246	$19.82	$19.80	$19.80
Purchase #6	$167.94	10.153%	$184.9909	$184.99	$185.00	$185.00
Purchase #7	$29.82	6.869%	$31.8683	$31.87	$31.85	$31.90
7 purchase totals =	$623.03		$678.8712	$678.87	$678.80	$678.90