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	$160.55	3.382%	$165.9798	$165.98	$166.00	$166.00
Purchase #2	$216.91	12.265%	$243.514	$243.51	$243.50	$243.50
Purchase #3	$59.57	5.262%	$62.7046	$62.70	$62.70	$62.70
Purchase #4	$131.84	13.223%	$149.2732	$149.27	$149.25	$149.30
Purchase #5	$177.38	8.705%	$192.8209	$192.82	$192.80	$192.80
Purchase #6	$245.39	12.807%	$276.8171	$276.82	$276.80	$276.80
Purchase #7	$122.84	7.311%	$131.8208	$131.82	$131.80	$131.80
7 purchase totals =	$1,114.48		$1,222.9304	$1,222.92	$1,222.85	$1,222.90