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	$92.28	7.681%	$99.368	$99.37	$99.35	$99.40
Purchase #2	$85.95	3.718%	$89.1456	$89.15	$89.15	$89.10
Purchase #3	$21.28	3.199%	$21.9607	$21.96	$21.95	$22.00
Purchase #4	$222.61	8.749%	$242.0861	$242.09	$242.10	$242.10
Purchase #5	$85.80	11.112%	$95.3341	$95.33	$95.35	$95.30
Purchase #6	$30.74	6.754%	$32.8162	$32.82	$32.80	$32.80
Purchase #7	$247.80	4.850%	$259.8183	$259.82	$259.80	$259.80
7 purchase totals =	$786.46		$840.5290	$840.54	$840.50	$840.50