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	$36.89	12.327%	$41.4374	$41.44	$41.45	$41.40
Purchase #2	$106.57	11.599%	$118.9311	$118.93	$118.95	$118.90
Purchase #3	$221.68	6.197%	$235.4175	$235.42	$235.40	$235.40
Purchase #4	$162.30	5.711%	$171.569	$171.57	$171.55	$171.60
Purchase #5	$187.34	7.185%	$200.8004	$200.80	$200.80	$200.80
Purchase #6	$71.91	9.248%	$78.5602	$78.56	$78.55	$78.60
Purchase #7	$20.90	13.653%	$23.7535	$23.75	$23.75	$23.80
7 purchase totals =	$807.59		$870.4691	$870.47	$870.45	$870.50