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	$22.59	6.107%	$23.9696	$23.97	$23.95	$24.00
Purchase #2	$174.76	9.373%	$191.1403	$191.14	$191.15	$191.10
Purchase #3	$184.88	3.742%	$191.7982	$191.80	$191.80	$191.80
Purchase #4	$36.32	7.827%	$39.1628	$39.16	$39.15	$39.20
Purchase #5	$196.48	13.805%	$223.6041	$223.60	$223.60	$223.60
Purchase #6	$222.69	4.765%	$233.3012	$233.30	$233.30	$233.30
Purchase #7	$48.69	9.293%	$53.2148	$53.21	$53.20	$53.20
7 purchase totals =	$886.41		$956.1910	$956.18	$956.15	$956.20