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	$107.80	11.813%	$120.5344	$120.53	$120.55	$120.50
Purchase #2	$71.79	10.181%	$79.0989	$79.10	$79.10	$79.10
Purchase #3	$160.91	6.351%	$171.1294	$171.13	$171.15	$171.10
Purchase #4	$232.52	13.401%	$263.68	$263.68	$263.70	$263.70
Purchase #5	$54.27	10.224%	$59.8186	$59.82	$59.80	$59.80
Purchase #6	$88.93	12.823%	$100.3335	$100.33	$100.35	$100.30
Purchase #7	$234.57	10.313%	$258.7612	$258.76	$258.75	$258.80
7 purchase totals =	$950.79		$1,053.3560	$1,053.35	$1,053.40	$1,053.30