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	$154.36	11.342%	$171.8675	$171.87	$171.85	$171.90
Purchase #2	$79.86	8.499%	$86.6473	$86.65	$86.65	$86.60
Purchase #3	$204.64	11.671%	$228.5235	$228.52	$228.50	$228.50
Purchase #4	$237.86	13.336%	$269.581	$269.58	$269.60	$269.60
Purchase #5	$82.42	8.577%	$89.4892	$89.49	$89.50	$89.50
Purchase #6	$202.91	9.793%	$222.781	$222.78	$222.80	$222.80
Purchase #7	$144.95	12.171%	$162.5919	$162.59	$162.60	$162.60
7 purchase totals =	$1,107.00		$1,231.4814	$1,231.48	$1,231.50	$1,231.50