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	$59.89	8.269%	$64.8423	$64.84	$64.85	$64.80
Purchase #2	$40.67	4.646%	$42.5595	$42.56	$42.55	$42.60
Purchase #3	$238.82	8.104%	$258.174	$258.17	$258.15	$258.20
Purchase #4	$52.58	11.808%	$58.7886	$58.79	$58.80	$58.80
Purchase #5	$142.50	11.818%	$159.3407	$159.34	$159.35	$159.30
Purchase #6	$124.40	13.846%	$141.6244	$141.62	$141.60	$141.60
Purchase #7	$80.32	6.667%	$85.6749	$85.67	$85.65	$85.70
7 purchase totals =	$739.18		$811.0044	$810.99	$810.95	$811.00