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	$160.99	6.671%	$171.7296	$171.73	$171.75	$171.70
Purchase #2	$87.89	13.292%	$99.5723	$99.57	$99.55	$99.60
Purchase #3	$57.30	7.565%	$61.6347	$61.63	$61.65	$61.60
Purchase #4	$179.34	5.866%	$189.8601	$189.86	$189.85	$189.90
Purchase #5	$52.37	11.527%	$58.4067	$58.41	$58.40	$58.40
Purchase #6	$32.33	5.111%	$33.9824	$33.98	$34.00	$34.00
Purchase #7	$95.84	13.267%	$108.5551	$108.56	$108.55	$108.60
7 purchase totals =	$666.06		$723.7409	$723.74	$723.75	$723.80