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	$101.61	11.121%	$112.91	$112.91	$112.90	$112.90
Purchase #2	$210.77	3.863%	$218.912	$218.91	$218.90	$218.90
Purchase #3	$84.92	11.157%	$94.3945	$94.39	$94.40	$94.40
Purchase #4	$210.49	5.525%	$222.1196	$222.12	$222.10	$222.10
Purchase #5	$80.79	3.150%	$83.3349	$83.33	$83.35	$83.30
Purchase #6	$81.54	3.174%	$84.1281	$84.13	$84.15	$84.10
Purchase #7	$250.69	13.656%	$284.9242	$284.92	$284.90	$284.90
7 purchase totals =	$1,020.81		$1,100.7233	$1,100.71	$1,100.70	$1,100.60