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	$102.27	4.752%	$107.1299	$107.13	$107.15	$107.10
Purchase #2	$94.54	11.749%	$105.6475	$105.65	$105.65	$105.60
Purchase #3	$167.98	13.849%	$191.2436	$191.24	$191.25	$191.20
Purchase #4	$209.35	6.701%	$223.3785	$223.38	$223.40	$223.40
Purchase #5	$50.88	10.131%	$56.0347	$56.03	$56.05	$56.00
Purchase #6	$87.59	4.203%	$91.2714	$91.27	$91.25	$91.30
Purchase #7	$131.87	5.439%	$139.0424	$139.04	$139.05	$139.00
7 purchase totals =	$844.48		$913.7480	$913.74	$913.80	$913.60