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	$95.57	4.657%	$100.0207	$100.02	$100.00	$100.00
Purchase #2	$158.93	4.311%	$165.7815	$165.78	$165.80	$165.80
Purchase #3	$97.76	10.764%	$108.2829	$108.28	$108.30	$108.30
Purchase #4	$211.78	12.759%	$238.801	$238.80	$238.80	$238.80
Purchase #5	$28.25	7.816%	$30.458	$30.46	$30.45	$30.50
Purchase #6	$163.68	4.841%	$171.6037	$171.60	$171.60	$171.60
Purchase #7	$245.89	11.465%	$274.0813	$274.08	$274.10	$274.10
7 purchase totals =	$1,001.86		$1,089.0291	$1,089.02	$1,089.05	$1,089.10