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	$240.88	5.162%	$253.3142	$253.31	$253.30	$253.30
Purchase #2	$178.72	11.550%	$199.3622	$199.36	$199.35	$199.40
Purchase #3	$96.37	9.802%	$105.8162	$105.82	$105.80	$105.80
Purchase #4	$99.78	5.192%	$104.9606	$104.96	$104.95	$105.00
Purchase #5	$18.93	9.234%	$20.678	$20.68	$20.70	$20.70
Purchase #6	$126.32	3.404%	$130.6199	$130.62	$130.60	$130.60
Purchase #7	$189.60	12.284%	$212.8905	$212.89	$212.90	$212.90
7 purchase totals =	$950.60		$1,027.6416	$1,027.64	$1,027.60	$1,027.70