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	$7.29	3.506%	$7.5456	$7.55	$7.55	$7.50
Purchase #2	$89.78	6.139%	$95.2916	$95.29	$95.30	$95.30
Purchase #3	$77.37	10.541%	$85.5256	$85.53	$85.55	$85.50
Purchase #4	$28.70	3.780%	$29.7849	$29.78	$29.80	$29.80
Purchase #5	$34.79	9.177%	$37.9827	$37.98	$38.00	$38.00
Purchase #6	$184.27	6.779%	$196.7617	$196.76	$196.75	$196.80
Purchase #7	$195.44	4.701%	$204.6276	$204.63	$204.65	$204.60
7 purchase totals =	$617.64		$657.5197	$657.52	$657.60	$657.50