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	$130.69	9.654%	$143.3068	$143.31	$143.30	$143.30
Purchase #2	$73.55	8.755%	$79.9893	$79.99	$80.00	$80.00
Purchase #3	$160.71	4.501%	$167.9436	$167.94	$167.95	$167.90
Purchase #4	$66.90	6.629%	$71.3348	$71.33	$71.35	$71.30
Purchase #5	$151.54	8.803%	$164.8801	$164.88	$164.90	$164.90
Purchase #6	$179.90	5.616%	$190.0032	$190.00	$190.00	$190.00
Purchase #7	$133.69	7.150%	$143.2488	$143.25	$143.25	$143.20
7 purchase totals =	$896.98		$960.7066	$960.70	$960.75	$960.60