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	$37.48	13.642%	$42.593	$42.59	$42.60	$42.60
Purchase #2	$31.70	9.663%	$34.7632	$34.76	$34.75	$34.80
Purchase #3	$93.54	6.794%	$99.8951	$99.90	$99.90	$99.90
Purchase #4	$211.88	3.391%	$219.0649	$219.06	$219.05	$219.10
Purchase #5	$185.37	13.621%	$210.6192	$210.62	$210.60	$210.60
Purchase #6	$126.61	7.631%	$136.2716	$136.27	$136.25	$136.30
Purchase #7	$189.93	12.399%	$213.4794	$213.48	$213.50	$213.50
7 purchase totals =	$876.51		$956.6864	$956.68	$956.65	$956.80