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	$155.81	8.184%	$168.5615	$168.56	$168.55	$168.60
Purchase #2	$51.61	6.356%	$54.8903	$54.89	$54.90	$54.90
Purchase #3	$16.94	12.298%	$19.0233	$19.02	$19.00	$19.00
Purchase #4	$61.50	6.498%	$65.4963	$65.50	$65.50	$65.50
Purchase #5	$25.51	11.490%	$28.4411	$28.44	$28.45	$28.40
Purchase #6	$222.26	12.848%	$250.816	$250.82	$250.80	$250.80
Purchase #7	$145.29	10.310%	$160.2694	$160.27	$160.25	$160.30
7 purchase totals =	$678.92		$747.4979	$747.50	$747.45	$747.50