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	$237.70	8.855%	$258.7483	$258.75	$258.75	$258.70
Purchase #2	$89.59	12.439%	$100.7341	$100.73	$100.75	$100.70
Purchase #3	$144.37	7.609%	$155.3551	$155.36	$155.35	$155.40
Purchase #4	$166.33	3.848%	$172.7304	$172.73	$172.75	$172.70
Purchase #5	$147.80	7.489%	$158.8687	$158.87	$158.85	$158.90
Purchase #6	$162.36	3.596%	$168.1985	$168.20	$168.20	$168.20
Purchase #7	$135.48	12.560%	$152.4963	$152.50	$152.50	$152.50
7 purchase totals =	$1,083.63		$1,167.1314	$1,167.14	$1,167.15	$1,167.10