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	$40.89	6.748%	$43.6493	$43.65	$43.65	$43.60
Purchase #2	$243.74	6.370%	$259.2662	$259.27	$259.25	$259.30
Purchase #3	$141.74	8.190%	$153.3485	$153.35	$153.35	$153.30
Purchase #4	$161.88	12.640%	$182.3416	$182.34	$182.35	$182.30
Purchase #5	$88.46	12.616%	$99.6201	$99.62	$99.60	$99.60
Purchase #6	$90.54	12.613%	$101.9598	$101.96	$101.95	$102.00
Purchase #7	$40.77	12.316%	$45.7912	$45.79	$45.80	$45.80
7 purchase totals =	$808.02		$885.9767	$885.98	$885.95	$885.90