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	$52.77	6.523%	$56.2122	$56.21	$56.20	$56.20
Purchase #2	$122.28	9.704%	$134.1461	$134.15	$134.15	$134.10
Purchase #3	$168.56	11.437%	$187.8382	$187.84	$187.85	$187.80
Purchase #4	$98.57	5.362%	$103.8553	$103.86	$103.85	$103.90
Purchase #5	$213.41	12.605%	$240.3103	$240.31	$240.30	$240.30
Purchase #6	$173.73	3.327%	$179.51	$179.51	$179.50	$179.50
Purchase #7	$97.69	5.550%	$103.1118	$103.11	$103.10	$103.10
7 purchase totals =	$927.01		$1,004.9839	$1,004.99	$1,004.95	$1,004.90