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	$76.94	3.380%	$79.5406	$79.54	$79.55	$79.50
Purchase #2	$188.30	11.415%	$209.7944	$209.79	$209.80	$209.80
Purchase #3	$145.89	13.494%	$165.5764	$165.58	$165.60	$165.60
Purchase #4	$50.97	6.768%	$54.4196	$54.42	$54.40	$54.40
Purchase #5	$90.25	7.145%	$96.6984	$96.70	$96.70	$96.70
Purchase #6	$228.77	8.571%	$248.3779	$248.38	$248.40	$248.40
Purchase #7	$145.37	7.223%	$155.8701	$155.87	$155.85	$155.90
7 purchase totals =	$926.49		$1,010.2774	$1,010.28	$1,010.30	$1,010.30