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	$37.51	13.553%	$42.5937	$42.59	$42.60	$42.60
Purchase #2	$99.46	5.479%	$104.9094	$104.91	$104.90	$104.90
Purchase #3	$174.70	13.495%	$198.2758	$198.28	$198.30	$198.30
Purchase #4	$82.46	12.646%	$92.8879	$92.89	$92.90	$92.90
Purchase #5	$185.95	13.689%	$211.4047	$211.40	$211.40	$211.40
Purchase #6	$35.44	7.421%	$38.07	$38.07	$38.05	$38.10
Purchase #7	$41.76	8.447%	$45.2875	$45.29	$45.30	$45.30
7 purchase totals =	$657.28		$733.4290	$733.43	$733.45	$733.50