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	$90.73	13.646%	$103.111	$103.11	$103.10	$103.10
Purchase #2	$142.55	11.553%	$159.0188	$159.02	$159.00	$159.00
Purchase #3	$123.40	7.699%	$132.9006	$132.90	$132.90	$132.90
Purchase #4	$39.77	5.502%	$41.9581	$41.96	$41.95	$42.00
Purchase #5	$89.45	11.783%	$99.9899	$99.99	$100.00	$100.00
Purchase #6	$16.73	9.142%	$18.2595	$18.26	$18.25	$18.30
Purchase #7	$213.82	9.115%	$233.3097	$233.31	$233.30	$233.30
7 purchase totals =	$716.45		$788.5476	$788.55	$788.50	$788.60