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	$108.39	3.500%	$112.1837	$112.18	$112.20	$112.20
Purchase #2	$41.61	4.274%	$43.3884	$43.39	$43.40	$43.40
Purchase #3	$100.96	13.259%	$114.3463	$114.35	$114.35	$114.30
Purchase #4	$135.74	10.774%	$150.3646	$150.36	$150.35	$150.40
Purchase #5	$222.69	6.400%	$236.9422	$236.94	$236.95	$236.90
Purchase #6	$55.87	6.506%	$59.5049	$59.50	$59.50	$59.50
Purchase #7	$29.65	8.670%	$32.2207	$32.22	$32.20	$32.20
7 purchase totals =	$694.91		$748.9508	$748.94	$748.95	$748.90