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	$250.40	11.187%	$278.4122	$278.41	$278.40	$278.40
Purchase #2	$235.36	3.821%	$244.3531	$244.35	$244.35	$244.40
Purchase #3	$99.96	10.351%	$110.3069	$110.31	$110.30	$110.30
Purchase #4	$151.81	5.611%	$160.3281	$160.33	$160.35	$160.30
Purchase #5	$89.98	12.365%	$101.106	$101.11	$101.10	$101.10
Purchase #6	$26.85	7.163%	$28.7733	$28.77	$28.75	$28.80
Purchase #7	$124.77	10.504%	$137.8758	$137.88	$137.90	$137.90
7 purchase totals =	$979.13		$1,061.1554	$1,061.16	$1,061.15	$1,061.20