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	$37.96	4.176%	$39.5452	$39.55	$39.55	$39.50
Purchase #2	$27.46	5.619%	$29.003	$29.00	$29.00	$29.00
Purchase #3	$36.81	13.654%	$41.836	$41.84	$41.85	$41.80
Purchase #4	$143.79	11.295%	$160.0311	$160.03	$160.05	$160.00
Purchase #5	$57.73	3.642%	$59.8325	$59.83	$59.85	$59.80
Purchase #6	$216.57	13.788%	$246.4307	$246.43	$246.45	$246.40
Purchase #7	$161.54	11.816%	$180.6276	$180.63	$180.65	$180.60
7 purchase totals =	$681.86		$757.3061	$757.31	$757.40	$757.10