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	$145.93	10.173%	$160.7755	$160.78	$160.80	$160.80
Purchase #2	$67.57	5.288%	$71.1431	$71.14	$71.15	$71.10
Purchase #3	$62.54	6.533%	$66.6257	$66.63	$66.65	$66.60
Purchase #4	$98.73	5.562%	$104.2214	$104.22	$104.20	$104.20
Purchase #5	$59.54	10.665%	$65.8899	$65.89	$65.90	$65.90
Purchase #6	$248.32	9.461%	$271.8136	$271.81	$271.80	$271.80
Purchase #7	$237.98	10.418%	$262.7728	$262.77	$262.75	$262.80
7 purchase totals =	$920.61		$1,003.2420	$1,003.24	$1,003.25	$1,003.20