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	$112.91	7.572%	$121.4595	$121.46	$121.45	$121.50
Purchase #2	$38.76	8.519%	$42.062	$42.06	$42.05	$42.10
Purchase #3	$122.74	12.216%	$137.7339	$137.73	$137.75	$137.70
Purchase #4	$201.36	13.167%	$227.8731	$227.87	$227.85	$227.90
Purchase #5	$189.29	11.811%	$211.647	$211.65	$211.65	$211.60
Purchase #6	$181.83	7.571%	$195.5963	$195.60	$195.60	$195.60
Purchase #7	$39.83	6.569%	$42.4464	$42.45	$42.45	$42.40
7 purchase totals =	$886.72		$978.8182	$978.82	$978.80	$978.80