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	$173.63	3.765%	$180.1672	$180.17	$180.15	$180.20
Purchase #2	$150.38	4.220%	$156.726	$156.73	$156.75	$156.70
Purchase #3	$163.38	13.105%	$184.7909	$184.79	$184.80	$184.80
Purchase #4	$116.28	11.781%	$129.9789	$129.98	$130.00	$130.00
Purchase #5	$84.64	5.804%	$89.5525	$89.55	$89.55	$89.60
Purchase #6	$37.79	11.220%	$42.03	$42.03	$42.05	$42.00
Purchase #7	$33.98	13.421%	$38.5405	$38.54	$38.55	$38.50
7 purchase totals =	$760.08		$821.7860	$821.79	$821.85	$821.80