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	$28.59	9.798%	$31.3912	$31.39	$31.40	$31.40
Purchase #2	$99.26	6.520%	$105.7318	$105.73	$105.75	$105.70
Purchase #3	$152.42	8.557%	$165.4626	$165.46	$165.45	$165.50
Purchase #4	$76.27	11.761%	$85.2401	$85.24	$85.25	$85.20
Purchase #5	$213.36	10.383%	$235.5132	$235.51	$235.50	$235.50
Purchase #6	$220.98	3.842%	$229.4701	$229.47	$229.45	$229.50
Purchase #7	$244.43	5.773%	$258.5409	$258.54	$258.55	$258.50
7 purchase totals =	$1,035.31		$1,111.3499	$1,111.34	$1,111.35	$1,111.30