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	$99.54	12.634%	$112.1159	$112.12	$112.10	$112.10
Purchase #2	$78.56	13.643%	$89.2779	$89.28	$89.30	$89.30
Purchase #3	$18.81	4.686%	$19.6914	$19.69	$19.70	$19.70
Purchase #4	$31.88	6.350%	$33.9044	$33.90	$33.90	$33.90
Purchase #5	$141.58	8.135%	$153.0975	$153.10	$153.10	$153.10
Purchase #6	$233.46	10.223%	$257.3266	$257.33	$257.35	$257.30
Purchase #7	$73.86	10.216%	$81.4055	$81.41	$81.40	$81.40
7 purchase totals =	$677.69		$746.8192	$746.83	$746.85	$746.80