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	$163.32	10.710%	$180.8116	$180.81	$180.80	$180.80
Purchase #2	$31.95	10.220%	$35.2153	$35.22	$35.20	$35.20
Purchase #3	$201.45	3.778%	$209.0608	$209.06	$209.05	$209.10
Purchase #4	$112.81	13.740%	$128.3101	$128.31	$128.30	$128.30
Purchase #5	$249.53	3.596%	$258.5031	$258.50	$258.50	$258.50
Purchase #6	$37.91	7.837%	$40.881	$40.88	$40.90	$40.90
Purchase #7	$216.52	10.276%	$238.7696	$238.77	$238.75	$238.80
7 purchase totals =	$1,013.49		$1,091.5515	$1,091.55	$1,091.50	$1,091.60