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	$38.93	6.502%	$41.4612	$41.46	$41.45	$41.50
Purchase #2	$219.35	5.453%	$231.3112	$231.31	$231.30	$231.30
Purchase #3	$230.58	9.226%	$251.8533	$251.85	$251.85	$251.90
Purchase #4	$171.34	5.404%	$180.5992	$180.60	$180.60	$180.60
Purchase #5	$51.33	13.236%	$58.124	$58.12	$58.10	$58.10
Purchase #6	$42.74	6.850%	$45.6677	$45.67	$45.65	$45.70
Purchase #7	$42.95	6.672%	$45.8156	$45.82	$45.80	$45.80
7 purchase totals =	$797.22		$854.8322	$854.83	$854.75	$854.90