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	$240.30	10.628%	$265.8391	$265.84	$265.85	$265.80
Purchase #2	$184.91	4.830%	$193.8412	$193.84	$193.85	$193.80
Purchase #3	$55.58	3.718%	$57.6465	$57.65	$57.65	$57.60
Purchase #4	$152.46	6.317%	$162.0909	$162.09	$162.10	$162.10
Purchase #5	$74.98	4.591%	$78.4223	$78.42	$78.40	$78.40
Purchase #6	$44.78	11.787%	$50.0582	$50.06	$50.05	$50.10
Purchase #7	$38.33	10.597%	$42.3918	$42.39	$42.40	$42.40
7 purchase totals =	$791.34		$850.2900	$850.29	$850.30	$850.20