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	$6.51	9.615%	$7.1359	$7.14	$7.15	$7.10
Purchase #2	$162.29	6.853%	$173.4117	$173.41	$173.40	$173.40
Purchase #3	$110.75	11.511%	$123.4984	$123.50	$123.50	$123.50
Purchase #4	$53.82	11.282%	$59.892	$59.89	$59.90	$59.90
Purchase #5	$65.30	9.402%	$71.4395	$71.44	$71.45	$71.40
Purchase #6	$173.34	6.672%	$184.9052	$184.91	$184.90	$184.90
Purchase #7	$63.97	5.444%	$67.4525	$67.45	$67.45	$67.50
7 purchase totals =	$635.98		$687.7352	$687.74	$687.75	$687.70