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	$96.45	13.385%	$109.3598	$109.36	$109.35	$109.40
Purchase #2	$47.83	7.105%	$51.2283	$51.23	$51.25	$51.20
Purchase #3	$167.43	6.662%	$178.5842	$178.58	$178.60	$178.60
Purchase #4	$236.54	13.489%	$268.4469	$268.45	$268.45	$268.40
Purchase #5	$19.94	12.557%	$22.4439	$22.44	$22.45	$22.40
Purchase #6	$35.25	11.385%	$39.2632	$39.26	$39.25	$39.30
Purchase #7	$82.36	10.429%	$90.9493	$90.95	$90.95	$90.90
7 purchase totals =	$685.80		$760.2756	$760.27	$760.30	$760.20