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	$186.30	13.619%	$211.6722	$211.67	$211.65	$211.70
Purchase #2	$201.56	13.533%	$228.8371	$228.84	$228.85	$228.80
Purchase #3	$150.41	10.221%	$165.7834	$165.78	$165.80	$165.80
Purchase #4	$152.39	10.797%	$168.8435	$168.84	$168.85	$168.80
Purchase #5	$158.56	10.873%	$175.8002	$175.80	$175.80	$175.80
Purchase #6	$128.90	11.579%	$143.8253	$143.83	$143.85	$143.80
Purchase #7	$89.41	4.573%	$93.4987	$93.50	$93.50	$93.50
7 purchase totals =	$1,067.53		$1,188.2604	$1,188.26	$1,188.30	$1,188.20