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	$189.48	8.124%	$204.8734	$204.87	$204.85	$204.90
Purchase #2	$111.91	6.344%	$119.0096	$119.01	$119.00	$119.00
Purchase #3	$32.34	13.135%	$36.5879	$36.59	$36.60	$36.60
Purchase #4	$35.86	6.375%	$38.1461	$38.15	$38.15	$38.10
Purchase #5	$196.82	11.205%	$218.8737	$218.87	$218.85	$218.90
Purchase #6	$147.36	3.340%	$152.2818	$152.28	$152.30	$152.30
Purchase #7	$82.40	8.308%	$89.2458	$89.25	$89.25	$89.20
7 purchase totals =	$796.17		$859.0183	$859.02	$859.00	$859.00