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	$217.44	3.666%	$225.4114	$225.41	$225.40	$225.40
Purchase #2	$142.53	12.614%	$160.5087	$160.51	$160.50	$160.50
Purchase #3	$43.33	13.182%	$49.0418	$49.04	$49.05	$49.00
Purchase #4	$55.82	6.826%	$59.6303	$59.63	$59.65	$59.60
Purchase #5	$128.57	13.492%	$145.9167	$145.92	$145.90	$145.90
Purchase #6	$210.39	12.550%	$236.7939	$236.79	$236.80	$236.80
Purchase #7	$34.47	9.581%	$37.7726	$37.77	$37.75	$37.80
7 purchase totals =	$832.55		$915.0754	$915.07	$915.05	$915.00