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	$74.73	4.415%	$78.0293	$78.03	$78.05	$78.00
Purchase #2	$237.35	8.174%	$256.751	$256.75	$256.75	$256.80
Purchase #3	$70.90	10.299%	$78.202	$78.20	$78.20	$78.20
Purchase #4	$53.56	3.193%	$55.2702	$55.27	$55.25	$55.30
Purchase #5	$90.44	9.424%	$98.9631	$98.96	$98.95	$99.00
Purchase #6	$227.49	7.509%	$244.5722	$244.57	$244.55	$244.60
Purchase #7	$139.47	12.538%	$156.9567	$156.96	$156.95	$157.00
7 purchase totals =	$893.94		$968.7445	$968.74	$968.70	$968.90