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	$9.96	6.296%	$10.5871	$10.59	$10.60	$10.60
Purchase #2	$145.68	12.790%	$164.3125	$164.31	$164.30	$164.30
Purchase #3	$34.53	7.622%	$37.1619	$37.16	$37.15	$37.20
Purchase #4	$115.49	8.355%	$125.1392	$125.14	$125.15	$125.10
Purchase #5	$71.71	6.801%	$76.587	$76.59	$76.60	$76.60
Purchase #6	$85.58	7.142%	$91.6921	$91.69	$91.70	$91.70
Purchase #7	$93.56	6.438%	$99.5834	$99.58	$99.60	$99.60
7 purchase totals =	$556.51		$605.0632	$605.06	$605.10	$605.10