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	$164.47	4.846%	$172.4402	$172.44	$172.45	$172.40
Purchase #2	$120.27	9.411%	$131.5886	$131.59	$131.60	$131.60
Purchase #3	$91.40	5.810%	$96.7103	$96.71	$96.70	$96.70
Purchase #4	$221.78	3.193%	$228.8614	$228.86	$228.85	$228.90
Purchase #5	$169.25	11.814%	$189.2452	$189.25	$189.25	$189.20
Purchase #6	$20.73	3.727%	$21.5026	$21.50	$21.50	$21.50
Purchase #7	$134.92	4.136%	$140.5003	$140.50	$140.50	$140.50
7 purchase totals =	$922.82		$980.8486	$980.85	$980.85	$980.80