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	$84.49	11.155%	$93.9149	$93.91	$93.90	$93.90
Purchase #2	$44.63	8.265%	$48.3187	$48.32	$48.30	$48.30
Purchase #3	$155.84	7.659%	$167.7758	$167.78	$167.80	$167.80
Purchase #4	$167.33	11.105%	$185.912	$185.91	$185.90	$185.90
Purchase #5	$148.47	11.569%	$165.6465	$165.65	$165.65	$165.60
Purchase #6	$111.91	6.580%	$119.2737	$119.27	$119.25	$119.30
Purchase #7	$125.25	13.548%	$142.2189	$142.22	$142.20	$142.20
7 purchase totals =	$837.92		$923.0605	$923.06	$923.00	$923.00