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	$26.48	7.689%	$28.516	$28.52	$28.50	$28.50
Purchase #2	$128.43	10.807%	$142.3094	$142.31	$142.30	$142.30
Purchase #3	$202.56	8.261%	$219.2935	$219.29	$219.30	$219.30
Purchase #4	$170.68	8.690%	$185.5121	$185.51	$185.50	$185.50
Purchase #5	$123.64	12.664%	$139.2978	$139.30	$139.30	$139.30
Purchase #6	$134.71	12.308%	$151.2901	$151.29	$151.30	$151.30
Purchase #7	$221.87	5.849%	$234.8472	$234.85	$234.85	$234.80
7 purchase totals =	$1,008.37		$1,101.0661	$1,101.07	$1,101.05	$1,101.00