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	$117.91	10.170%	$129.9014	$129.90	$129.90	$129.90
Purchase #2	$84.99	5.747%	$89.8744	$89.87	$89.85	$89.90
Purchase #3	$165.81	3.330%	$171.3315	$171.33	$171.35	$171.30
Purchase #4	$151.46	6.634%	$161.5079	$161.51	$161.50	$161.50
Purchase #5	$207.80	5.172%	$218.5474	$218.55	$218.55	$218.50
Purchase #6	$169.88	12.172%	$190.5578	$190.56	$190.55	$190.60
Purchase #7	$242.54	8.153%	$262.3143	$262.31	$262.30	$262.30
7 purchase totals =	$1,140.39		$1,224.0347	$1,224.03	$1,224.00	$1,224.00