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	$98.39	11.123%	$109.3339	$109.33	$109.35	$109.30
Purchase #2	$199.92	9.734%	$219.3802	$219.38	$219.40	$219.40
Purchase #3	$53.46	10.149%	$58.8857	$58.89	$58.90	$58.90
Purchase #4	$143.64	3.843%	$149.1601	$149.16	$149.15	$149.20
Purchase #5	$51.98	7.444%	$55.8494	$55.85	$55.85	$55.80
Purchase #6	$245.37	12.254%	$275.4376	$275.44	$275.45	$275.40
Purchase #7	$211.67	5.685%	$223.7034	$223.70	$223.70	$223.70
7 purchase totals =	$1,004.43		$1,091.7503	$1,091.75	$1,091.80	$1,091.70