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	$47.73	6.684%	$50.9203	$50.92	$50.90	$50.90
Purchase #2	$79.33	7.869%	$85.5725	$85.57	$85.55	$85.60
Purchase #3	$117.84	12.501%	$132.5712	$132.57	$132.55	$132.60
Purchase #4	$99.66	4.817%	$104.4606	$104.46	$104.45	$104.50
Purchase #5	$198.59	10.407%	$219.2573	$219.26	$219.25	$219.30
Purchase #6	$222.92	8.701%	$242.3163	$242.32	$242.30	$242.30
Purchase #7	$10.60	7.628%	$11.4086	$11.41	$11.40	$11.40
7 purchase totals =	$776.67		$846.5068	$846.51	$846.40	$846.60