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	$78.86	13.463%	$89.4769	$89.48	$89.50	$89.50
Purchase #2	$243.96	5.119%	$256.4483	$256.45	$256.45	$256.40
Purchase #3	$80.57	6.567%	$85.861	$85.86	$85.85	$85.90
Purchase #4	$124.29	5.636%	$131.295	$131.30	$131.30	$131.30
Purchase #5	$98.72	4.874%	$103.5316	$103.53	$103.55	$103.50
Purchase #6	$99.99	13.769%	$113.7576	$113.76	$113.75	$113.80
Purchase #7	$56.98	13.485%	$64.6638	$64.66	$64.65	$64.70
7 purchase totals =	$783.37		$845.0342	$845.04	$845.05	$845.10