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	$139.76	5.321%	$147.1966	$147.20	$147.20	$147.20
Purchase #2	$101.26	7.437%	$108.7907	$108.79	$108.80	$108.80
Purchase #3	$189.71	3.664%	$196.661	$196.66	$196.65	$196.70
Purchase #4	$224.42	7.185%	$240.5446	$240.54	$240.55	$240.50
Purchase #5	$48.32	11.408%	$53.8323	$53.83	$53.85	$53.80
Purchase #6	$247.75	13.243%	$280.5595	$280.56	$280.55	$280.60
Purchase #7	$66.73	6.616%	$71.1449	$71.14	$71.15	$71.10
7 purchase totals =	$1,017.95		$1,098.7296	$1,098.72	$1,098.75	$1,098.70