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	$65.48	9.761%	$71.8715	$71.87	$71.85	$71.90
Purchase #2	$54.57	7.728%	$58.7872	$58.79	$58.80	$58.80
Purchase #3	$35.39	5.783%	$37.4366	$37.44	$37.45	$37.40
Purchase #4	$106.57	9.472%	$116.6643	$116.66	$116.65	$116.70
Purchase #5	$165.65	9.454%	$181.3106	$181.31	$181.30	$181.30
Purchase #6	$62.33	5.418%	$65.707	$65.71	$65.70	$65.70
Purchase #7	$6.66	13.300%	$7.5458	$7.55	$7.55	$7.50
7 purchase totals =	$496.65		$539.3230	$539.33	$539.30	$539.30