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	$39.59	6.604%	$42.2045	$42.20	$42.20	$42.20
Purchase #2	$176.36	8.632%	$191.5834	$191.58	$191.60	$191.60
Purchase #3	$23.48	3.400%	$24.2783	$24.28	$24.30	$24.30
Purchase #4	$78.91	9.337%	$86.2778	$86.28	$86.30	$86.30
Purchase #5	$155.30	10.418%	$171.4792	$171.48	$171.50	$171.50
Purchase #6	$137.49	9.303%	$150.2807	$150.28	$150.30	$150.30
Purchase #7	$51.83	11.180%	$57.6246	$57.62	$57.60	$57.60
7 purchase totals =	$662.96		$723.7285	$723.72	$723.80	$723.80