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	$30.27	10.672%	$33.5004	$33.50	$33.50	$33.50
Purchase #2	$59.38	4.415%	$62.0016	$62.00	$62.00	$62.00
Purchase #3	$123.53	4.331%	$128.8801	$128.88	$128.90	$128.90
Purchase #4	$133.94	6.125%	$142.1438	$142.14	$142.15	$142.10
Purchase #5	$140.66	8.336%	$152.3854	$152.39	$152.40	$152.40
Purchase #6	$123.49	5.729%	$130.5647	$130.56	$130.55	$130.60
Purchase #7	$9.40	6.571%	$10.0177	$10.02	$10.00	$10.00
7 purchase totals =	$620.67		$659.4937	$659.49	$659.50	$659.50