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	$243.79	9.825%	$267.7424	$267.74	$267.75	$267.70
Purchase #2	$23.47	3.602%	$24.3154	$24.32	$24.30	$24.30
Purchase #3	$72.88	11.340%	$81.1446	$81.14	$81.15	$81.10
Purchase #4	$70.31	11.323%	$78.2712	$78.27	$78.25	$78.30
Purchase #5	$6.63	10.370%	$7.3175	$7.32	$7.30	$7.30
Purchase #6	$63.28	13.655%	$71.9209	$71.92	$71.90	$71.90
Purchase #7	$141.50	8.284%	$153.2219	$153.22	$153.20	$153.20
7 purchase totals =	$621.86		$683.9339	$683.93	$683.85	$683.80