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	$47.47	6.402%	$50.509	$50.51	$50.50	$50.50
Purchase #2	$44.31	7.405%	$47.5912	$47.59	$47.60	$47.60
Purchase #3	$218.62	7.851%	$235.7839	$235.78	$235.80	$235.80
Purchase #4	$222.73	9.808%	$244.5754	$244.58	$244.60	$244.60
Purchase #5	$28.96	11.491%	$32.2878	$32.29	$32.30	$32.30
Purchase #6	$167.89	7.806%	$180.9955	$181.00	$181.00	$181.00
Purchase #7	$54.77	9.263%	$59.8433	$59.84	$59.85	$59.80
7 purchase totals =	$784.75		$851.5861	$851.59	$851.65	$851.60