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	$115.89	13.330%	$131.3381	$131.34	$131.35	$131.30
Purchase #2	$136.72	7.787%	$147.3664	$147.37	$147.35	$147.40
Purchase #3	$247.66	3.300%	$255.8328	$255.83	$255.85	$255.80
Purchase #4	$221.91	9.720%	$243.4797	$243.48	$243.50	$243.50
Purchase #5	$149.34	12.571%	$168.1135	$168.11	$168.10	$168.10
Purchase #6	$106.95	4.283%	$111.5307	$111.53	$111.55	$111.50
Purchase #7	$241.48	10.487%	$266.804	$266.80	$266.80	$266.80
7 purchase totals =	$1,219.95		$1,324.4652	$1,324.46	$1,324.50	$1,324.40