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	$109.27	12.870%	$123.333	$123.33	$123.35	$123.30
Purchase #2	$116.91	12.477%	$131.4969	$131.50	$131.50	$131.50
Purchase #3	$109.79	12.706%	$123.7399	$123.74	$123.75	$123.70
Purchase #4	$195.36	4.444%	$204.0418	$204.04	$204.05	$204.00
Purchase #5	$145.33	5.573%	$153.4292	$153.43	$153.45	$153.40
Purchase #6	$88.80	8.239%	$96.1162	$96.12	$96.10	$96.10
Purchase #7	$90.95	8.853%	$99.0018	$99.00	$99.00	$99.00
7 purchase totals =	$856.41		$931.1588	$931.16	$931.20	$931.00