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	$236.80	7.225%	$253.9088	$253.91	$253.90	$253.90
Purchase #2	$41.61	6.481%	$44.3067	$44.31	$44.30	$44.30
Purchase #3	$85.25	11.814%	$95.3214	$95.32	$95.30	$95.30
Purchase #4	$43.67	7.210%	$46.8186	$46.82	$46.80	$46.80
Purchase #5	$45.27	3.472%	$46.8418	$46.84	$46.85	$46.80
Purchase #6	$91.71	11.621%	$102.3676	$102.37	$102.35	$102.40
Purchase #7	$31.58	5.484%	$33.3118	$33.31	$33.30	$33.30
7 purchase totals =	$575.89		$622.8767	$622.88	$622.80	$622.80