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	$156.89	3.750%	$162.7734	$162.77	$162.75	$162.80
Purchase #2	$137.91	5.701%	$145.7722	$145.77	$145.75	$145.80
Purchase #3	$71.54	9.277%	$78.1768	$78.18	$78.20	$78.20
Purchase #4	$228.41	13.606%	$259.4875	$259.49	$259.50	$259.50
Purchase #5	$161.54	13.508%	$183.3608	$183.36	$183.35	$183.40
Purchase #6	$198.62	12.193%	$222.8377	$222.84	$222.85	$222.80
Purchase #7	$51.79	8.345%	$56.1119	$56.11	$56.10	$56.10
7 purchase totals =	$1,006.70		$1,108.5203	$1,108.52	$1,108.50	$1,108.60