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	$11.41	8.549%	$12.3854	$12.39	$12.40	$12.40
Purchase #2	$157.55	6.840%	$168.3264	$168.33	$168.35	$168.30
Purchase #3	$88.69	7.332%	$95.1928	$95.19	$95.20	$95.20
Purchase #4	$208.51	6.552%	$222.1716	$222.17	$222.15	$222.20
Purchase #5	$147.40	5.390%	$155.3449	$155.34	$155.35	$155.30
Purchase #6	$145.48	6.108%	$154.3659	$154.37	$154.35	$154.40
Purchase #7	$187.55	3.795%	$194.6675	$194.67	$194.65	$194.70
7 purchase totals =	$946.59		$1,002.4545	$1,002.46	$1,002.45	$1,002.50