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	$29.35	12.479%	$33.0126	$33.01	$33.00	$33.00
Purchase #2	$154.88	6.808%	$165.4242	$165.42	$165.40	$165.40
Purchase #3	$166.45	13.328%	$188.6345	$188.63	$188.65	$188.60
Purchase #4	$159.35	3.375%	$164.7281	$164.73	$164.75	$164.70
Purchase #5	$159.37	7.786%	$171.7785	$171.78	$171.80	$171.80
Purchase #6	$104.66	7.131%	$112.1233	$112.12	$112.10	$112.10
Purchase #7	$128.90	9.403%	$141.0205	$141.02	$141.00	$141.00
7 purchase totals =	$902.96		$976.7217	$976.71	$976.70	$976.60