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	$45.51	5.860%	$48.1769	$48.18	$48.20	$48.20
Purchase #2	$142.83	11.309%	$158.9826	$158.98	$159.00	$159.00
Purchase #3	$56.33	13.514%	$63.9424	$63.94	$63.95	$63.90
Purchase #4	$40.44	11.483%	$45.0837	$45.08	$45.10	$45.10
Purchase #5	$98.56	10.764%	$109.169	$109.17	$109.15	$109.20
Purchase #6	$237.58	7.865%	$256.2657	$256.27	$256.25	$256.30
Purchase #7	$62.90	10.853%	$69.7265	$69.73	$69.75	$69.70
7 purchase totals =	$684.15		$751.3468	$751.35	$751.40	$751.40