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	$98.80	7.765%	$106.4718	$106.47	$106.45	$106.50
Purchase #2	$86.83	7.188%	$93.0713	$93.07	$93.05	$93.10
Purchase #3	$133.52	6.589%	$142.3176	$142.32	$142.30	$142.30
Purchase #4	$110.79	7.828%	$119.4626	$119.46	$119.45	$119.50
Purchase #5	$177.50	7.109%	$190.1185	$190.12	$190.10	$190.10
Purchase #6	$148.97	10.500%	$164.6119	$164.61	$164.60	$164.60
Purchase #7	$80.70	12.335%	$90.6543	$90.65	$90.65	$90.70
7 purchase totals =	$837.11		$906.7080	$906.70	$906.60	$906.80