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	$84.33	5.735%	$89.1663	$89.17	$89.15	$89.20
Purchase #2	$209.81	10.429%	$231.6911	$231.69	$231.70	$231.70
Purchase #3	$186.34	13.251%	$211.0319	$211.03	$211.05	$211.00
Purchase #4	$244.88	8.576%	$265.8809	$265.88	$265.90	$265.90
Purchase #5	$51.60	7.261%	$55.3467	$55.35	$55.35	$55.30
Purchase #6	$119.97	13.678%	$136.3795	$136.38	$136.40	$136.40
Purchase #7	$99.52	9.699%	$109.1724	$109.17	$109.15	$109.20
7 purchase totals =	$996.45		$1,098.6688	$1,098.67	$1,098.70	$1,098.70