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	$222.57	11.554%	$248.2857	$248.29	$248.30	$248.30
Purchase #2	$174.44	4.286%	$181.9165	$181.92	$181.90	$181.90
Purchase #3	$232.80	6.220%	$247.2802	$247.28	$247.30	$247.30
Purchase #4	$78.54	4.590%	$82.145	$82.15	$82.15	$82.10
Purchase #5	$218.74	3.851%	$227.1637	$227.16	$227.15	$227.20
Purchase #6	$172.43	5.250%	$181.4826	$181.48	$181.50	$181.50
Purchase #7	$157.61	8.842%	$171.5459	$171.55	$171.55	$171.50
7 purchase totals =	$1,257.13		$1,339.8196	$1,339.83	$1,339.85	$1,339.80