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	$85.46	7.126%	$91.5499	$91.55	$91.55	$91.50
Purchase #2	$240.27	12.774%	$270.9621	$270.96	$270.95	$271.00
Purchase #3	$100.82	12.620%	$113.5435	$113.54	$113.55	$113.50
Purchase #4	$100.35	11.507%	$111.8973	$111.90	$111.90	$111.90
Purchase #5	$217.36	13.301%	$246.2711	$246.27	$246.25	$246.30
Purchase #6	$247.32	13.209%	$279.9885	$279.99	$280.00	$280.00
Purchase #7	$19.76	4.336%	$20.6168	$20.62	$20.60	$20.60
7 purchase totals =	$1,011.34		$1,134.8292	$1,134.83	$1,134.80	$1,134.80