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	$18.72	7.107%	$20.0504	$20.05	$20.05	$20.10
Purchase #2	$91.71	7.828%	$98.8891	$98.89	$98.90	$98.90
Purchase #3	$102.48	6.622%	$109.2662	$109.27	$109.25	$109.30
Purchase #4	$207.56	9.335%	$226.9357	$226.94	$226.95	$226.90
Purchase #5	$103.58	11.831%	$115.8345	$115.83	$115.85	$115.80
Purchase #6	$78.31	10.165%	$86.2702	$86.27	$86.25	$86.30
Purchase #7	$72.67	10.446%	$80.2611	$80.26	$80.25	$80.30
7 purchase totals =	$675.03		$737.5072	$737.51	$737.50	$737.60