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	$44.49	13.287%	$50.4014	$50.40	$50.40	$50.40
Purchase #2	$81.39	12.693%	$91.7208	$91.72	$91.70	$91.70
Purchase #3	$82.77	8.455%	$89.7682	$89.77	$89.75	$89.80
Purchase #4	$79.99	12.400%	$89.9088	$89.91	$89.90	$89.90
Purchase #5	$194.40	9.723%	$213.3015	$213.30	$213.30	$213.30
Purchase #6	$22.39	9.411%	$24.4971	$24.50	$24.50	$24.50
Purchase #7	$196.25	7.296%	$210.5684	$210.57	$210.55	$210.60
7 purchase totals =	$701.68		$770.1662	$770.17	$770.10	$770.20