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	$78.61	6.741%	$83.9091	$83.91	$83.90	$83.90
Purchase #2	$250.46	11.233%	$278.5942	$278.59	$278.60	$278.60
Purchase #3	$125.84	9.612%	$137.9357	$137.94	$137.95	$137.90
Purchase #4	$233.38	10.323%	$257.4718	$257.47	$257.45	$257.50
Purchase #5	$35.72	11.159%	$39.706	$39.71	$39.70	$39.70
Purchase #6	$47.96	7.218%	$51.4218	$51.42	$51.40	$51.40
Purchase #7	$199.98	4.644%	$209.2671	$209.27	$209.25	$209.30
7 purchase totals =	$971.95		$1,058.3057	$1,058.31	$1,058.25	$1,058.30