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	$89.83	11.414%	$100.0832	$100.08	$100.10	$100.10
Purchase #2	$228.68	11.250%	$254.4065	$254.41	$254.40	$254.40
Purchase #3	$157.39	9.478%	$172.3074	$172.31	$172.30	$172.30
Purchase #4	$196.77	8.484%	$213.464	$213.46	$213.45	$213.50
Purchase #5	$129.96	5.834%	$137.5419	$137.54	$137.55	$137.50
Purchase #6	$177.93	6.770%	$189.9759	$189.98	$190.00	$190.00
Purchase #7	$26.41	8.557%	$28.6699	$28.67	$28.65	$28.70
7 purchase totals =	$1,006.97		$1,096.4488	$1,096.45	$1,096.45	$1,096.50