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	$112.33	7.417%	$120.6615	$120.66	$120.65	$120.70
Purchase #2	$94.64	3.799%	$98.2354	$98.24	$98.25	$98.20
Purchase #3	$33.65	10.374%	$37.1409	$37.14	$37.15	$37.10
Purchase #4	$189.45	11.249%	$210.7612	$210.76	$210.75	$210.80
Purchase #5	$192.71	6.548%	$205.3287	$205.33	$205.35	$205.30
Purchase #6	$171.75	11.337%	$191.2213	$191.22	$191.20	$191.20
Purchase #7	$98.36	13.179%	$111.3229	$111.32	$111.30	$111.30
7 purchase totals =	$892.89		$974.6719	$974.67	$974.65	$974.60