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	$39.86	6.530%	$42.4629	$42.46	$42.45	$42.50
Purchase #2	$212.98	11.602%	$237.6899	$237.69	$237.70	$237.70
Purchase #3	$232.90	13.603%	$264.5814	$264.58	$264.60	$264.60
Purchase #4	$197.78	7.148%	$211.9173	$211.92	$211.90	$211.90
Purchase #5	$111.91	5.864%	$118.4724	$118.47	$118.45	$118.50
Purchase #6	$65.72	8.547%	$71.3371	$71.34	$71.35	$71.30
Purchase #7	$70.63	5.706%	$74.6601	$74.66	$74.65	$74.70
7 purchase totals =	$931.78		$1,021.1211	$1,021.12	$1,021.10	$1,021.20