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	$81.53	5.775%	$86.2384	$86.24	$86.25	$86.20
Purchase #2	$118.95	10.542%	$131.4897	$131.49	$131.50	$131.50
Purchase #3	$89.34	11.339%	$99.4703	$99.47	$99.45	$99.50
Purchase #4	$237.45	11.290%	$264.2581	$264.26	$264.25	$264.30
Purchase #5	$160.90	12.765%	$181.4389	$181.44	$181.45	$181.40
Purchase #6	$65.81	10.445%	$72.6839	$72.68	$72.70	$72.70
Purchase #7	$90.87	12.873%	$102.5677	$102.57	$102.55	$102.60
7 purchase totals =	$844.85		$938.1470	$938.15	$938.15	$938.20