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	$82.97	7.561%	$89.2434	$89.24	$89.25	$89.20
Purchase #2	$191.90	13.561%	$217.9236	$217.92	$217.90	$217.90
Purchase #3	$96.47	11.732%	$107.7879	$107.79	$107.80	$107.80
Purchase #4	$189.51	12.822%	$213.809	$213.81	$213.80	$213.80
Purchase #5	$151.81	6.231%	$161.2693	$161.27	$161.25	$161.30
Purchase #6	$250.74	10.682%	$277.524	$277.52	$277.50	$277.50
Purchase #7	$11.45	11.399%	$12.7552	$12.76	$12.75	$12.80
7 purchase totals =	$974.85		$1,080.3124	$1,080.31	$1,080.25	$1,080.30