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	$83.92	6.435%	$89.3203	$89.32	$89.30	$89.30
Purchase #2	$7.30	10.707%	$8.0816	$8.08	$8.10	$8.10
Purchase #3	$246.94	12.738%	$278.3952	$278.40	$278.40	$278.40
Purchase #4	$111.56	10.618%	$123.4054	$123.41	$123.40	$123.40
Purchase #5	$61.34	10.609%	$67.8476	$67.85	$67.85	$67.80
Purchase #6	$212.82	3.628%	$220.5411	$220.54	$220.55	$220.50
Purchase #7	$191.55	7.561%	$206.0331	$206.03	$206.05	$206.00
7 purchase totals =	$915.43		$993.6243	$993.63	$993.65	$993.50