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	$126.36	12.432%	$142.0691	$142.07	$142.05	$142.10
Purchase #2	$37.40	12.677%	$42.1412	$42.14	$42.15	$42.10
Purchase #3	$34.37	4.114%	$35.784	$35.78	$35.80	$35.80
Purchase #4	$77.89	10.212%	$85.8441	$85.84	$85.85	$85.80
Purchase #5	$168.92	10.818%	$187.1938	$187.19	$187.20	$187.20
Purchase #6	$84.50	13.392%	$95.8162	$95.82	$95.80	$95.80
Purchase #7	$247.36	11.270%	$275.2375	$275.24	$275.25	$275.20
7 purchase totals =	$776.80		$864.0859	$864.08	$864.10	$864.00