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	$89.57	12.530%	$100.7931	$100.79	$100.80	$100.80
Purchase #2	$224.92	9.330%	$245.905	$245.91	$245.90	$245.90
Purchase #3	$109.30	12.340%	$122.7876	$122.79	$122.80	$122.80
Purchase #4	$147.88	11.839%	$165.3875	$165.39	$165.40	$165.40
Purchase #5	$135.97	5.800%	$143.8563	$143.86	$143.85	$143.90
Purchase #6	$191.62	10.608%	$211.947	$211.95	$211.95	$211.90
Purchase #7	$97.77	5.834%	$103.4739	$103.47	$103.45	$103.50
7 purchase totals =	$997.03		$1,094.1504	$1,094.16	$1,094.15	$1,094.20