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	$114.30	12.808%	$128.9395	$128.94	$128.95	$128.90
Purchase #2	$99.86	9.401%	$109.2478	$109.25	$109.25	$109.20
Purchase #3	$33.37	3.111%	$34.4081	$34.41	$34.40	$34.40
Purchase #4	$177.31	4.578%	$185.4273	$185.43	$185.45	$185.40
Purchase #5	$148.80	11.774%	$166.3197	$166.32	$166.30	$166.30
Purchase #6	$71.67	9.202%	$78.2651	$78.27	$78.25	$78.30
Purchase #7	$48.91	3.688%	$50.7138	$50.71	$50.70	$50.70
7 purchase totals =	$694.22		$753.3213	$753.33	$753.30	$753.20