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	$42.83	9.238%	$46.7866	$46.79	$46.80	$46.80
Purchase #2	$171.80	3.551%	$177.9006	$177.90	$177.90	$177.90
Purchase #3	$140.86	4.234%	$146.824	$146.82	$146.80	$146.80
Purchase #4	$102.89	11.223%	$114.4373	$114.44	$114.45	$114.40
Purchase #5	$175.28	3.769%	$181.8863	$181.89	$181.90	$181.90
Purchase #6	$28.49	11.814%	$31.8558	$31.86	$31.85	$31.90
Purchase #7	$48.57	6.168%	$51.5658	$51.57	$51.55	$51.60
7 purchase totals =	$710.72		$751.2564	$751.27	$751.25	$751.30