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	$27.37	13.403%	$31.0384	$31.04	$31.05	$31.00
Purchase #2	$249.72	11.609%	$278.71	$278.71	$278.70	$278.70
Purchase #3	$172.94	13.594%	$196.4495	$196.45	$196.45	$196.40
Purchase #4	$152.35	4.791%	$159.6491	$159.65	$159.65	$159.60
Purchase #5	$92.25	3.296%	$95.2906	$95.29	$95.30	$95.30
Purchase #6	$131.89	4.392%	$137.6826	$137.68	$137.70	$137.70
Purchase #7	$169.76	11.490%	$189.2654	$189.27	$189.25	$189.30
7 purchase totals =	$996.28		$1,088.0856	$1,088.09	$1,088.10	$1,088.00