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	$189.84	11.623%	$211.9051	$211.91	$211.90	$211.90
Purchase #2	$109.27	6.370%	$116.2305	$116.23	$116.25	$116.20
Purchase #3	$141.43	7.544%	$152.0995	$152.10	$152.10	$152.10
Purchase #4	$199.27	11.530%	$222.2458	$222.25	$222.25	$222.20
Purchase #5	$105.66	8.688%	$114.8397	$114.84	$114.85	$114.80
Purchase #6	$106.76	13.554%	$121.2303	$121.23	$121.25	$121.20
Purchase #7	$128.84	12.417%	$144.8381	$144.84	$144.85	$144.80
7 purchase totals =	$981.07		$1,083.3890	$1,083.40	$1,083.45	$1,083.20