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	$39.55	8.212%	$42.7978	$42.80	$42.80	$42.80
Purchase #2	$197.70	10.698%	$218.8499	$218.85	$218.85	$218.80
Purchase #3	$200.90	3.811%	$208.5563	$208.56	$208.55	$208.60
Purchase #4	$186.83	11.633%	$208.5639	$208.56	$208.55	$208.60
Purchase #5	$89.93	7.839%	$96.9796	$96.98	$97.00	$97.00
Purchase #6	$152.39	13.635%	$173.1684	$173.17	$173.15	$173.20
Purchase #7	$83.89	7.134%	$89.8747	$89.87	$89.85	$89.90
7 purchase totals =	$951.19		$1,038.7906	$1,038.79	$1,038.75	$1,038.90