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	$95.59	9.331%	$104.5095	$104.51	$104.50	$104.50
Purchase #2	$91.77	4.522%	$95.9198	$95.92	$95.90	$95.90
Purchase #3	$52.28	11.715%	$58.4046	$58.40	$58.40	$58.40
Purchase #4	$248.98	12.807%	$280.8669	$280.87	$280.85	$280.90
Purchase #5	$53.98	3.507%	$55.8731	$55.87	$55.85	$55.90
Purchase #6	$103.51	9.802%	$113.6561	$113.66	$113.65	$113.70
Purchase #7	$203.37	12.518%	$228.8279	$228.83	$228.85	$228.80
7 purchase totals =	$849.48		$938.0579	$938.06	$938.00	$938.10