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	$109.47	10.480%	$120.9425	$120.94	$120.95	$120.90
Purchase #2	$172.86	3.867%	$179.5445	$179.54	$179.55	$179.50
Purchase #3	$95.32	6.488%	$101.5044	$101.50	$101.50	$101.50
Purchase #4	$89.87	10.111%	$98.9568	$98.96	$98.95	$99.00
Purchase #5	$184.29	4.140%	$191.9196	$191.92	$191.90	$191.90
Purchase #6	$72.54	7.282%	$77.8224	$77.82	$77.80	$77.80
Purchase #7	$144.65	4.559%	$151.2446	$151.24	$151.25	$151.20
7 purchase totals =	$869.00		$921.9348	$921.92	$921.90	$921.80