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	$94.33	4.272%	$98.3598	$98.36	$98.35	$98.40
Purchase #2	$130.69	6.765%	$139.5312	$139.53	$139.55	$139.50
Purchase #3	$157.68	9.643%	$172.8851	$172.89	$172.90	$172.90
Purchase #4	$62.68	12.412%	$70.4598	$70.46	$70.45	$70.50
Purchase #5	$195.39	12.677%	$220.1596	$220.16	$220.15	$220.20
Purchase #6	$80.96	10.524%	$89.4802	$89.48	$89.50	$89.50
Purchase #7	$46.90	7.188%	$50.2712	$50.27	$50.25	$50.30
7 purchase totals =	$768.63		$841.1469	$841.15	$841.15	$841.30