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	$136.94	4.792%	$143.5022	$143.50	$143.50	$143.50
Purchase #2	$242.43	7.574%	$260.7916	$260.79	$260.80	$260.80
Purchase #3	$98.58	3.516%	$102.0461	$102.05	$102.05	$102.00
Purchase #4	$131.97	3.693%	$136.8437	$136.84	$136.85	$136.80
Purchase #5	$244.40	6.316%	$259.8363	$259.84	$259.85	$259.80
Purchase #6	$123.30	3.743%	$127.9151	$127.92	$127.90	$127.90
Purchase #7	$67.26	8.475%	$72.9603	$72.96	$72.95	$73.00
7 purchase totals =	$1,044.88		$1,103.8953	$1,103.90	$1,103.90	$1,103.80