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	$139.50	12.531%	$156.9807	$156.98	$157.00	$157.00
Purchase #2	$171.79	8.280%	$186.0142	$186.01	$186.00	$186.00
Purchase #3	$76.90	11.298%	$85.5882	$85.59	$85.60	$85.60
Purchase #4	$86.64	11.517%	$96.6183	$96.62	$96.60	$96.60
Purchase #5	$36.67	11.365%	$40.8375	$40.84	$40.85	$40.80
Purchase #6	$125.73	4.401%	$131.2634	$131.26	$131.25	$131.30
Purchase #7	$248.29	4.671%	$259.8876	$259.89	$259.90	$259.90
7 purchase totals =	$885.52		$957.1899	$957.19	$957.20	$957.20