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	$39.69	8.646%	$43.1216	$43.12	$43.10	$43.10
Purchase #2	$91.36	11.850%	$102.1862	$102.19	$102.20	$102.20
Purchase #3	$213.28	4.386%	$222.6345	$222.63	$222.65	$222.60
Purchase #4	$51.53	3.168%	$53.1625	$53.16	$53.15	$53.20
Purchase #5	$82.54	11.104%	$91.7052	$91.71	$91.70	$91.70
Purchase #6	$111.60	7.793%	$120.297	$120.30	$120.30	$120.30
Purchase #7	$20.73	5.190%	$21.8059	$21.81	$21.80	$21.80
7 purchase totals =	$610.73		$654.9129	$654.92	$654.90	$654.90