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	$29.42	13.397%	$33.3614	$33.36	$33.35	$33.40
Purchase #2	$159.41	6.520%	$169.8035	$169.80	$169.80	$169.80
Purchase #3	$103.44	9.474%	$113.2399	$113.24	$113.25	$113.20
Purchase #4	$121.99	5.234%	$128.375	$128.38	$128.40	$128.40
Purchase #5	$151.31	9.735%	$166.04	$166.04	$166.05	$166.00
Purchase #6	$175.42	12.269%	$196.9423	$196.94	$196.95	$196.90
Purchase #7	$63.67	12.765%	$71.7975	$71.80	$71.80	$71.80
7 purchase totals =	$804.66		$879.5596	$879.56	$879.60	$879.50