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	$154.85	11.138%	$172.0972	$172.10	$172.10	$172.10
Purchase #2	$16.30	11.737%	$18.2131	$18.21	$18.20	$18.20
Purchase #3	$85.87	6.368%	$91.3382	$91.34	$91.35	$91.30
Purchase #4	$39.66	4.705%	$41.526	$41.53	$41.55	$41.50
Purchase #5	$185.46	5.437%	$195.5435	$195.54	$195.55	$195.50
Purchase #6	$96.50	11.740%	$107.8291	$107.83	$107.85	$107.80
Purchase #7	$39.97	13.817%	$45.4927	$45.49	$45.50	$45.50
7 purchase totals =	$618.61		$672.0398	$672.04	$672.10	$671.90