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	$66.48	6.792%	$70.9953	$71.00	$71.00	$71.00
Purchase #2	$221.29	10.772%	$245.1274	$245.13	$245.15	$245.10
Purchase #3	$81.92	13.278%	$92.7973	$92.80	$92.80	$92.80
Purchase #4	$196.88	13.443%	$223.3466	$223.35	$223.35	$223.30
Purchase #5	$164.78	6.514%	$175.5138	$175.51	$175.50	$175.50
Purchase #6	$194.74	11.641%	$217.4097	$217.41	$217.40	$217.40
Purchase #7	$219.60	12.870%	$247.8625	$247.86	$247.85	$247.90
7 purchase totals =	$1,145.69		$1,273.0526	$1,273.06	$1,273.05	$1,273.00