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	$89.44	10.703%	$99.0128	$99.01	$99.00	$99.00
Purchase #2	$36.62	6.586%	$39.0318	$39.03	$39.05	$39.00
Purchase #3	$199.62	11.410%	$222.3966	$222.40	$222.40	$222.40
Purchase #4	$198.47	9.302%	$216.9317	$216.93	$216.95	$216.90
Purchase #5	$158.96	5.347%	$167.4596	$167.46	$167.45	$167.50
Purchase #6	$159.94	7.119%	$171.3261	$171.33	$171.35	$171.30
Purchase #7	$145.62	12.662%	$164.0584	$164.06	$164.05	$164.10
7 purchase totals =	$988.67		$1,080.2170	$1,080.22	$1,080.25	$1,080.20