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	$36.37	6.704%	$38.8082	$38.81	$38.80	$38.80
Purchase #2	$232.82	12.596%	$262.146	$262.15	$262.15	$262.10
Purchase #3	$75.62	12.710%	$85.2313	$85.23	$85.25	$85.20
Purchase #4	$224.88	4.288%	$234.5229	$234.52	$234.50	$234.50
Purchase #5	$59.82	13.483%	$67.8855	$67.89	$67.90	$67.90
Purchase #6	$138.36	9.674%	$151.7449	$151.74	$151.75	$151.70
Purchase #7	$118.62	10.174%	$130.6884	$130.69	$130.70	$130.70
7 purchase totals =	$886.49		$971.0272	$971.03	$971.05	$970.90