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	$170.47	10.225%	$187.9006	$187.90	$187.90	$187.90
Purchase #2	$72.75	10.504%	$80.3917	$80.39	$80.40	$80.40
Purchase #3	$190.25	10.318%	$209.88	$209.88	$209.90	$209.90
Purchase #4	$222.37	12.830%	$250.9001	$250.90	$250.90	$250.90
Purchase #5	$192.29	4.328%	$200.6123	$200.61	$200.60	$200.60
Purchase #6	$170.74	7.621%	$183.7521	$183.75	$183.75	$183.80
Purchase #7	$109.27	3.223%	$112.7918	$112.79	$112.80	$112.80
7 purchase totals =	$1,128.14		$1,226.2286	$1,226.22	$1,226.25	$1,226.30