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	$24.93	8.238%	$26.9837	$26.98	$27.00	$27.00
Purchase #2	$117.89	13.665%	$133.9997	$134.00	$134.00	$134.00
Purchase #3	$193.43	7.695%	$208.3144	$208.31	$208.30	$208.30
Purchase #4	$105.38	3.748%	$109.3296	$109.33	$109.35	$109.30
Purchase #5	$78.76	13.174%	$89.1358	$89.14	$89.15	$89.10
Purchase #6	$115.25	6.494%	$122.7343	$122.73	$122.75	$122.70
Purchase #7	$190.69	7.700%	$205.3731	$205.37	$205.35	$205.40
7 purchase totals =	$826.33		$895.8706	$895.86	$895.90	$895.80