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	$55.51	3.803%	$57.621	$57.62	$57.60	$57.60
Purchase #2	$72.42	6.377%	$77.0382	$77.04	$77.05	$77.00
Purchase #3	$86.45	6.217%	$91.8246	$91.82	$91.80	$91.80
Purchase #4	$41.89	9.556%	$45.893	$45.89	$45.90	$45.90
Purchase #5	$50.49	4.384%	$52.7035	$52.70	$52.70	$52.70
Purchase #6	$37.94	7.270%	$40.6982	$40.70	$40.70	$40.70
Purchase #7	$130.73	13.190%	$147.9733	$147.97	$147.95	$148.00
7 purchase totals =	$475.43		$513.7518	$513.74	$513.70	$513.70