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	$98.66	10.740%	$109.2561	$109.26	$109.25	$109.30
Purchase #2	$238.45	10.724%	$264.0214	$264.02	$264.00	$264.00
Purchase #3	$142.72	9.626%	$156.4582	$156.46	$156.45	$156.50
Purchase #4	$11.50	10.719%	$12.7327	$12.73	$12.75	$12.70
Purchase #5	$111.50	4.773%	$116.8219	$116.82	$116.80	$116.80
Purchase #6	$201.95	4.189%	$210.4097	$210.41	$210.40	$210.40
Purchase #7	$79.98	13.155%	$90.5014	$90.50	$90.50	$90.50
7 purchase totals =	$884.76		$960.2014	$960.20	$960.15	$960.20