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	$229.46	9.591%	$251.4675	$251.47	$251.45	$251.50
Purchase #2	$178.69	11.292%	$198.8677	$198.87	$198.85	$198.90
Purchase #3	$148.64	6.642%	$158.5127	$158.51	$158.50	$158.50
Purchase #4	$73.75	5.790%	$78.0201	$78.02	$78.00	$78.00
Purchase #5	$12.73	13.459%	$14.4433	$14.44	$14.45	$14.40
Purchase #6	$38.46	4.758%	$40.2899	$40.29	$40.30	$40.30
Purchase #7	$73.48	4.311%	$76.6477	$76.65	$76.65	$76.60
7 purchase totals =	$755.21		$818.2489	$818.25	$818.20	$818.20