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	$142.86	12.800%	$161.1461	$161.15	$161.15	$161.10
Purchase #2	$198.70	6.309%	$211.236	$211.24	$211.25	$211.20
Purchase #3	$141.41	12.166%	$158.6139	$158.61	$158.60	$158.60
Purchase #4	$169.52	9.483%	$185.5956	$185.60	$185.60	$185.60
Purchase #5	$187.91	11.728%	$209.9481	$209.95	$209.95	$209.90
Purchase #6	$174.65	12.303%	$196.1372	$196.14	$196.15	$196.10
Purchase #7	$32.90	13.609%	$37.3774	$37.38	$37.40	$37.40
7 purchase totals =	$1,047.95		$1,160.0543	$1,160.07	$1,160.10	$1,159.90