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	$51.80	7.261%	$55.5612	$55.56	$55.55	$55.60
Purchase #2	$145.32	11.822%	$162.4997	$162.50	$162.50	$162.50
Purchase #3	$97.64	3.455%	$101.0135	$101.01	$101.00	$101.00
Purchase #4	$25.91	9.157%	$28.2826	$28.28	$28.30	$28.30
Purchase #5	$165.60	10.399%	$182.8207	$182.82	$182.80	$182.80
Purchase #6	$71.45	4.819%	$74.8932	$74.89	$74.90	$74.90
Purchase #7	$56.49	4.118%	$58.8163	$58.82	$58.80	$58.80
7 purchase totals =	$614.21		$663.8872	$663.88	$663.85	$663.90