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	$201.54	8.272%	$218.2114	$218.21	$218.20	$218.20
Purchase #2	$50.81	7.700%	$54.7224	$54.72	$54.70	$54.70
Purchase #3	$178.92	6.379%	$190.3333	$190.33	$190.35	$190.30
Purchase #4	$36.67	8.175%	$39.6678	$39.67	$39.65	$39.70
Purchase #5	$169.93	8.435%	$184.2636	$184.26	$184.25	$184.30
Purchase #6	$218.86	6.540%	$233.1734	$233.17	$233.15	$233.20
Purchase #7	$153.27	4.743%	$160.5396	$160.54	$160.55	$160.50
7 purchase totals =	$1,010.00		$1,080.9115	$1,080.90	$1,080.85	$1,080.90