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	$79.92	11.763%	$89.321	$89.32	$89.30	$89.30
Purchase #2	$197.49	6.165%	$209.6653	$209.67	$209.65	$209.70
Purchase #3	$61.28	9.405%	$67.0434	$67.04	$67.05	$67.00
Purchase #4	$242.39	11.119%	$269.3413	$269.34	$269.35	$269.30
Purchase #5	$174.31	6.533%	$185.6977	$185.70	$185.70	$185.70
Purchase #6	$63.46	3.708%	$65.8131	$65.81	$65.80	$65.80
Purchase #7	$205.38	5.600%	$216.8813	$216.88	$216.90	$216.90
7 purchase totals =	$1,024.23		$1,103.7631	$1,103.76	$1,103.75	$1,103.70