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	$102.30	8.197%	$110.6855	$110.69	$110.70	$110.70
Purchase #2	$124.56	11.486%	$138.867	$138.87	$138.85	$138.90
Purchase #3	$109.69	13.847%	$124.8788	$124.88	$124.90	$124.90
Purchase #4	$106.65	5.280%	$112.2811	$112.28	$112.30	$112.30
Purchase #5	$199.72	5.808%	$211.3197	$211.32	$211.30	$211.30
Purchase #6	$36.39	10.366%	$40.1622	$40.16	$40.15	$40.20
Purchase #7	$90.70	9.481%	$99.2993	$99.30	$99.30	$99.30
7 purchase totals =	$770.01		$837.4936	$837.50	$837.50	$837.60