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	$178.99	12.220%	$200.8626	$200.86	$200.85	$200.90
Purchase #2	$234.89	4.573%	$245.6315	$245.63	$245.65	$245.60
Purchase #3	$59.94	5.562%	$63.2739	$63.27	$63.25	$63.30
Purchase #4	$131.27	8.371%	$142.2586	$142.26	$142.25	$142.30
Purchase #5	$33.31	4.196%	$34.7077	$34.71	$34.70	$34.70
Purchase #6	$95.90	8.771%	$104.3114	$104.31	$104.30	$104.30
Purchase #7	$77.47	7.373%	$83.1819	$83.18	$83.20	$83.20
7 purchase totals =	$811.77		$874.2276	$874.22	$874.20	$874.30