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	$185.55	12.629%	$208.9831	$208.98	$209.00	$209.00
Purchase #2	$150.96	13.612%	$171.5087	$171.51	$171.50	$171.50
Purchase #3	$207.34	7.471%	$222.8304	$222.83	$222.85	$222.80
Purchase #4	$63.77	12.252%	$71.5831	$71.58	$71.60	$71.60
Purchase #5	$191.29	11.435%	$213.164	$213.16	$213.15	$213.20
Purchase #6	$84.67	6.243%	$89.9559	$89.96	$89.95	$90.00
Purchase #7	$95.80	8.174%	$103.6307	$103.63	$103.65	$103.60
7 purchase totals =	$979.38		$1,081.6559	$1,081.65	$1,081.70	$1,081.70