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	$242.80	13.438%	$275.4275	$275.43	$275.45	$275.40
Purchase #2	$196.87	4.663%	$206.05	$206.05	$206.05	$206.10
Purchase #3	$189.82	4.520%	$198.3999	$198.40	$198.40	$198.40
Purchase #4	$25.92	4.281%	$27.0296	$27.03	$27.05	$27.00
Purchase #5	$26.83	11.842%	$30.0072	$30.01	$30.00	$30.00
Purchase #6	$80.93	12.138%	$90.7533	$90.75	$90.75	$90.80
Purchase #7	$103.62	7.364%	$111.2506	$111.25	$111.25	$111.30
7 purchase totals =	$866.79		$938.9181	$938.92	$938.95	$939.00