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	$21.33	6.407%	$22.6966	$22.70	$22.70	$22.70
Purchase #2	$200.94	12.355%	$225.7661	$225.77	$225.75	$225.80
Purchase #3	$99.76	4.210%	$103.9599	$103.96	$103.95	$104.00
Purchase #4	$101.38	11.379%	$112.916	$112.92	$112.90	$112.90
Purchase #5	$55.90	7.819%	$60.2708	$60.27	$60.25	$60.30
Purchase #6	$41.41	3.559%	$42.8838	$42.88	$42.90	$42.90
Purchase #7	$85.58	13.847%	$97.4303	$97.43	$97.45	$97.40
7 purchase totals =	$606.30		$665.9235	$665.93	$665.90	$666.00