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	$104.63	13.355%	$118.6033	$118.60	$118.60	$118.60
Purchase #2	$25.87	6.352%	$27.5133	$27.51	$27.50	$27.50
Purchase #3	$86.53	4.567%	$90.4818	$90.48	$90.50	$90.50
Purchase #4	$157.35	10.806%	$174.3532	$174.35	$174.35	$174.40
Purchase #5	$221.54	3.788%	$229.9319	$229.93	$229.95	$229.90
Purchase #6	$137.89	7.538%	$148.2841	$148.28	$148.30	$148.30
Purchase #7	$54.48	12.295%	$61.1783	$61.18	$61.20	$61.20
7 purchase totals =	$788.29		$850.3459	$850.33	$850.40	$850.40