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	$5.77	13.795%	$6.566	$6.57	$6.55	$6.60
Purchase #2	$88.81	13.732%	$101.0054	$101.01	$101.00	$101.00
Purchase #3	$54.56	9.625%	$59.8114	$59.81	$59.80	$59.80
Purchase #4	$30.51	8.496%	$33.1021	$33.10	$33.10	$33.10
Purchase #5	$62.29	8.294%	$67.4563	$67.46	$67.45	$67.50
Purchase #6	$28.89	10.133%	$31.8174	$31.82	$31.80	$31.80
Purchase #7	$145.62	7.625%	$156.7235	$156.72	$156.70	$156.70
7 purchase totals =	$416.45		$456.4821	$456.49	$456.40	$456.50