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	$207.80	6.456%	$221.2156	$221.22	$221.20	$221.20
Purchase #2	$158.71	6.645%	$169.2563	$169.26	$169.25	$169.30
Purchase #3	$37.90	11.154%	$42.1274	$42.13	$42.15	$42.10
Purchase #4	$53.84	8.165%	$58.236	$58.24	$58.25	$58.20
Purchase #5	$37.59	7.108%	$40.2619	$40.26	$40.25	$40.30
Purchase #6	$37.39	5.578%	$39.4756	$39.48	$39.50	$39.50
Purchase #7	$51.48	6.326%	$54.7366	$54.74	$54.75	$54.70
7 purchase totals =	$584.71		$625.3094	$625.33	$625.35	$625.30