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	$186.26	7.398%	$200.0395	$200.04	$200.05	$200.00
Purchase #2	$245.61	11.282%	$273.3197	$273.32	$273.30	$273.30
Purchase #3	$12.47	3.609%	$12.92	$12.92	$12.90	$12.90
Purchase #4	$101.97	11.185%	$113.3753	$113.38	$113.40	$113.40
Purchase #5	$211.85	7.281%	$227.2748	$227.27	$227.25	$227.30
Purchase #6	$69.97	13.508%	$79.4215	$79.42	$79.40	$79.40
Purchase #7	$67.43	7.319%	$72.3652	$72.37	$72.35	$72.40
7 purchase totals =	$895.56		$978.7160	$978.72	$978.65	$978.70