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	$76.58	5.124%	$80.504	$80.50	$80.50	$80.50
Purchase #2	$165.51	3.553%	$171.3906	$171.39	$171.40	$171.40
Purchase #3	$20.80	7.181%	$22.2936	$22.29	$22.30	$22.30
Purchase #4	$76.42	13.126%	$86.4509	$86.45	$86.45	$86.50
Purchase #5	$60.40	11.485%	$67.3369	$67.34	$67.35	$67.30
Purchase #6	$76.45	7.744%	$82.3703	$82.37	$82.35	$82.40
Purchase #7	$119.46	13.485%	$135.5692	$135.57	$135.55	$135.60
7 purchase totals =	$595.62		$645.9155	$645.91	$645.90	$646.00