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	$93.34	5.802%	$98.7556	$98.76	$98.75	$98.80
Purchase #2	$183.43	11.847%	$205.161	$205.16	$205.15	$205.20
Purchase #3	$185.51	10.498%	$204.9848	$204.98	$205.00	$205.00
Purchase #4	$35.87	12.655%	$40.4093	$40.41	$40.40	$40.40
Purchase #5	$215.62	5.365%	$227.188	$227.19	$227.20	$227.20
Purchase #6	$249.28	12.522%	$280.4948	$280.49	$280.50	$280.50
Purchase #7	$226.44	7.441%	$243.2894	$243.29	$243.30	$243.30
7 purchase totals =	$1,189.49		$1,300.2829	$1,300.28	$1,300.30	$1,300.40