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	$41.82	13.664%	$47.5343	$47.53	$47.55	$47.50
Purchase #2	$146.67	4.152%	$152.7597	$152.76	$152.75	$152.80
Purchase #3	$248.49	5.340%	$261.7594	$261.76	$261.75	$261.80
Purchase #4	$92.63	11.701%	$103.4686	$103.47	$103.45	$103.50
Purchase #5	$66.27	7.584%	$71.2959	$71.30	$71.30	$71.30
Purchase #6	$235.51	11.154%	$261.7788	$261.78	$261.80	$261.80
Purchase #7	$139.93	12.430%	$157.3233	$157.32	$157.30	$157.30
7 purchase totals =	$971.32		$1,055.9200	$1,055.92	$1,055.90	$1,056.00