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	$26.92	4.712%	$28.1885	$28.19	$28.20	$28.20
Purchase #2	$104.44	12.387%	$117.377	$117.38	$117.40	$117.40
Purchase #3	$88.96	11.817%	$99.4724	$99.47	$99.45	$99.50
Purchase #4	$182.88	7.396%	$196.4058	$196.41	$196.40	$196.40
Purchase #5	$87.89	5.522%	$92.7433	$92.74	$92.75	$92.70
Purchase #6	$80.28	10.396%	$88.6259	$88.63	$88.65	$88.60
Purchase #7	$76.80	7.368%	$82.4586	$82.46	$82.45	$82.50
7 purchase totals =	$648.17		$705.2715	$705.28	$705.30	$705.30