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	$106.62	12.654%	$120.1117	$120.11	$120.10	$120.10
Purchase #2	$172.80	8.566%	$187.602	$187.60	$187.60	$187.60
Purchase #3	$57.29	6.172%	$60.8259	$60.83	$60.85	$60.80
Purchase #4	$105.60	7.212%	$113.2159	$113.22	$113.20	$113.20
Purchase #5	$40.50	4.647%	$42.382	$42.38	$42.40	$42.40
Purchase #6	$194.84	7.736%	$209.9128	$209.91	$209.90	$209.90
Purchase #7	$29.36	11.811%	$32.8277	$32.83	$32.85	$32.80
7 purchase totals =	$707.01		$766.8780	$766.88	$766.90	$766.80