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	$72.33	10.467%	$79.9008	$79.90	$79.90	$79.90
Purchase #2	$240.75	6.256%	$255.8113	$255.81	$255.80	$255.80
Purchase #3	$188.80	11.546%	$210.5988	$210.60	$210.60	$210.60
Purchase #4	$215.34	12.538%	$242.3393	$242.34	$242.35	$242.30
Purchase #5	$64.77	11.621%	$72.2969	$72.30	$72.30	$72.30
Purchase #6	$96.56	5.136%	$101.5193	$101.52	$101.50	$101.50
Purchase #7	$234.92	10.124%	$258.7033	$258.70	$258.70	$258.70
7 purchase totals =	$1,113.47		$1,221.1697	$1,221.17	$1,221.15	$1,221.10