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	$114.89	12.679%	$129.4569	$129.46	$129.45	$129.50
Purchase #2	$197.74	13.500%	$224.4349	$224.43	$224.45	$224.40
Purchase #3	$28.47	9.569%	$31.1943	$31.19	$31.20	$31.20
Purchase #4	$86.36	4.144%	$89.9388	$89.94	$89.95	$89.90
Purchase #5	$24.76	12.369%	$27.8226	$27.82	$27.80	$27.80
Purchase #6	$83.84	7.662%	$90.2638	$90.26	$90.25	$90.30
Purchase #7	$78.74	7.800%	$84.8817	$84.88	$84.90	$84.90
7 purchase totals =	$614.80		$677.9930	$677.98	$678.00	$678.00