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	$28.73	4.122%	$29.9143	$29.91	$29.90	$29.90
Purchase #2	$79.46	11.109%	$88.2872	$88.29	$88.30	$88.30
Purchase #3	$62.53	11.365%	$69.6365	$69.64	$69.65	$69.60
Purchase #4	$90.77	11.386%	$101.1051	$101.11	$101.10	$101.10
Purchase #5	$239.36	13.316%	$271.2332	$271.23	$271.25	$271.20
Purchase #6	$177.86	10.273%	$196.1316	$196.13	$196.15	$196.10
Purchase #7	$203.52	9.512%	$222.8788	$222.88	$222.90	$222.90
7 purchase totals =	$882.23		$979.1867	$979.19	$979.25	$979.10