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	$60.93	11.403%	$67.8778	$67.88	$67.90	$67.90
Purchase #2	$78.83	8.819%	$85.782	$85.78	$85.80	$85.80
Purchase #3	$86.42	13.706%	$98.2647	$98.26	$98.25	$98.30
Purchase #4	$236.30	12.352%	$265.4878	$265.49	$265.50	$265.50
Purchase #5	$142.70	5.528%	$150.5885	$150.59	$150.60	$150.60
Purchase #6	$91.31	5.223%	$96.0791	$96.08	$96.10	$96.10
Purchase #7	$110.67	9.215%	$120.8682	$120.87	$120.85	$120.90
7 purchase totals =	$807.16		$884.9481	$884.95	$885.00	$885.10