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	$71.34	9.115%	$77.8426	$77.84	$77.85	$77.80
Purchase #2	$110.60	3.772%	$114.7718	$114.77	$114.75	$114.80
Purchase #3	$61.67	4.601%	$64.5074	$64.51	$64.50	$64.50
Purchase #4	$35.53	7.424%	$38.1677	$38.17	$38.15	$38.20
Purchase #5	$64.54	9.563%	$70.712	$70.71	$70.70	$70.70
Purchase #6	$18.97	11.727%	$21.1946	$21.19	$21.20	$21.20
Purchase #7	$98.30	13.516%	$111.5862	$111.59	$111.60	$111.60
7 purchase totals =	$460.95		$498.7823	$498.78	$498.75	$498.80