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	$9.67	3.869%	$10.0441	$10.04	$10.05	$10.00
Purchase #2	$126.64	4.145%	$131.8892	$131.89	$131.90	$131.90
Purchase #3	$170.36	7.650%	$183.3925	$183.39	$183.40	$183.40
Purchase #4	$46.81	8.600%	$50.8357	$50.84	$50.85	$50.80
Purchase #5	$36.53	6.229%	$38.8055	$38.81	$38.80	$38.80
Purchase #6	$209.45	6.371%	$222.7941	$222.79	$222.80	$222.80
Purchase #7	$136.48	8.333%	$147.8529	$147.85	$147.85	$147.90
7 purchase totals =	$735.94		$785.6140	$785.61	$785.65	$785.60