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	$88.71	12.253%	$99.5796	$99.58	$99.60	$99.60
Purchase #2	$172.82	9.805%	$189.765	$189.77	$189.75	$189.80
Purchase #3	$239.49	12.705%	$269.9172	$269.92	$269.90	$269.90
Purchase #4	$77.79	3.858%	$80.7911	$80.79	$80.80	$80.80
Purchase #5	$21.74	13.734%	$24.7258	$24.73	$24.75	$24.70
Purchase #6	$37.83	12.671%	$42.6234	$42.62	$42.60	$42.60
Purchase #7	$31.33	11.661%	$34.9834	$34.98	$35.00	$35.00
7 purchase totals =	$669.71		$742.3855	$742.39	$742.40	$742.40