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	$103.65	4.315%	$108.1225	$108.12	$108.10	$108.10
Purchase #2	$102.36	8.657%	$111.2213	$111.22	$111.20	$111.20
Purchase #3	$80.32	13.711%	$91.3327	$91.33	$91.35	$91.30
Purchase #4	$182.78	4.820%	$191.59	$191.59	$191.60	$191.60
Purchase #5	$34.95	12.841%	$39.4379	$39.44	$39.45	$39.40
Purchase #6	$71.44	10.402%	$78.8712	$78.87	$78.85	$78.90
Purchase #7	$98.30	12.746%	$110.8293	$110.83	$110.85	$110.80
7 purchase totals =	$673.80		$731.4049	$731.40	$731.40	$731.30