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	$63.94	5.869%	$67.6926	$67.69	$67.70	$67.70
Purchase #2	$120.68	13.763%	$137.2892	$137.29	$137.30	$137.30
Purchase #3	$54.61	4.736%	$57.1963	$57.20	$57.20	$57.20
Purchase #4	$141.84	7.512%	$152.495	$152.50	$152.50	$152.50
Purchase #5	$17.89	4.582%	$18.7097	$18.71	$18.70	$18.70
Purchase #6	$7.99	6.159%	$8.4821	$8.48	$8.50	$8.50
Purchase #7	$78.85	13.748%	$89.6903	$89.69	$89.70	$89.70
7 purchase totals =	$485.80		$531.5552	$531.56	$531.60	$531.60