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	$77.50	3.692%	$80.3613	$80.36	$80.35	$80.40
Purchase #2	$150.83	8.661%	$163.8934	$163.89	$163.90	$163.90
Purchase #3	$210.76	11.506%	$235.01	$235.01	$235.00	$235.00
Purchase #4	$150.77	13.831%	$171.623	$171.62	$171.60	$171.60
Purchase #5	$74.33	10.457%	$82.1027	$82.10	$82.10	$82.10
Purchase #6	$141.32	9.663%	$154.9758	$154.98	$155.00	$155.00
Purchase #7	$195.98	8.105%	$211.8642	$211.86	$211.85	$211.90
7 purchase totals =	$1,001.49		$1,099.8304	$1,099.82	$1,099.80	$1,099.90