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	$121.98	8.772%	$132.6801	$132.68	$132.70	$132.70
Purchase #2	$178.99	7.520%	$192.45	$192.45	$192.45	$192.50
Purchase #3	$220.30	11.366%	$245.3393	$245.34	$245.35	$245.30
Purchase #4	$41.89	3.469%	$43.3432	$43.34	$43.35	$43.30
Purchase #5	$74.81	8.179%	$80.9287	$80.93	$80.95	$80.90
Purchase #6	$18.48	9.477%	$20.2313	$20.23	$20.25	$20.20
Purchase #7	$42.44	7.413%	$45.5861	$45.59	$45.60	$45.60
7 purchase totals =	$698.89		$760.5587	$760.56	$760.65	$760.50