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	$231.66	10.199%	$255.287	$255.29	$255.30	$255.30
Purchase #2	$235.67	9.659%	$258.4334	$258.43	$258.45	$258.40
Purchase #3	$208.61	6.791%	$222.7767	$222.78	$222.80	$222.80
Purchase #4	$163.96	3.505%	$169.7068	$169.71	$169.70	$169.70
Purchase #5	$213.84	7.159%	$229.1488	$229.15	$229.15	$229.10
Purchase #6	$89.32	11.242%	$99.3614	$99.36	$99.35	$99.40
Purchase #7	$84.89	6.838%	$90.6948	$90.69	$90.70	$90.70
7 purchase totals =	$1,227.95		$1,325.4089	$1,325.41	$1,325.45	$1,325.40