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	$114.86	5.227%	$120.8637	$120.86	$120.85	$120.90
Purchase #2	$91.63	9.160%	$100.0233	$100.02	$100.00	$100.00
Purchase #3	$80.78	11.571%	$90.1271	$90.13	$90.15	$90.10
Purchase #4	$209.55	11.668%	$234.0003	$234.00	$234.00	$234.00
Purchase #5	$108.58	5.261%	$114.2924	$114.29	$114.30	$114.30
Purchase #6	$215.98	12.302%	$242.5499	$242.55	$242.55	$242.50
Purchase #7	$128.31	8.223%	$138.8609	$138.86	$138.85	$138.90
7 purchase totals =	$949.69		$1,040.7176	$1,040.71	$1,040.70	$1,040.70