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	$237.61	5.595%	$250.9043	$250.90	$250.90	$250.90
Purchase #2	$234.66	12.454%	$263.8846	$263.88	$263.90	$263.90
Purchase #3	$93.86	11.511%	$104.6642	$104.66	$104.65	$104.70
Purchase #4	$57.50	9.108%	$62.7371	$62.74	$62.75	$62.70
Purchase #5	$89.33	10.488%	$98.6989	$98.70	$98.70	$98.70
Purchase #6	$166.51	4.124%	$173.3769	$173.38	$173.40	$173.40
Purchase #7	$120.33	8.472%	$130.5244	$130.52	$130.50	$130.50
7 purchase totals =	$999.80		$1,084.7904	$1,084.78	$1,084.80	$1,084.80