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	$74.60	4.581%	$78.0174	$78.02	$78.00	$78.00
Purchase #2	$195.89	6.403%	$208.4328	$208.43	$208.45	$208.40
Purchase #3	$79.74	11.455%	$88.8742	$88.87	$88.85	$88.90
Purchase #4	$37.35	13.802%	$42.505	$42.51	$42.50	$42.50
Purchase #5	$105.38	12.809%	$118.8781	$118.88	$118.90	$118.90
Purchase #6	$46.48	13.353%	$52.6865	$52.69	$52.70	$52.70
Purchase #7	$181.47	12.149%	$203.5168	$203.52	$203.50	$203.50
7 purchase totals =	$720.91		$792.9108	$792.92	$792.90	$792.90