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	$82.97	7.618%	$89.2907	$89.29	$89.30	$89.30
Purchase #2	$105.39	5.156%	$110.8239	$110.82	$110.80	$110.80
Purchase #3	$25.82	9.810%	$28.3529	$28.35	$28.35	$28.40
Purchase #4	$211.71	10.451%	$233.8358	$233.84	$233.85	$233.80
Purchase #5	$198.32	10.818%	$219.7743	$219.77	$219.75	$219.80
Purchase #6	$139.32	5.596%	$147.1163	$147.12	$147.10	$147.10
Purchase #7	$104.87	13.300%	$118.8177	$118.82	$118.80	$118.80
7 purchase totals =	$868.40		$948.0116	$948.01	$947.95	$948.00