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	$188.25	6.476%	$200.4411	$200.44	$200.45	$200.40
Purchase #2	$59.50	7.803%	$64.1428	$64.14	$64.15	$64.10
Purchase #3	$250.78	10.658%	$277.5081	$277.51	$277.50	$277.50
Purchase #4	$85.70	12.163%	$96.1237	$96.12	$96.10	$96.10
Purchase #5	$11.61	12.443%	$13.0546	$13.05	$13.05	$13.10
Purchase #6	$232.83	12.821%	$262.6811	$262.68	$262.70	$262.70
Purchase #7	$237.70	7.648%	$255.8793	$255.88	$255.90	$255.90
7 purchase totals =	$1,066.37		$1,169.8307	$1,169.82	$1,169.85	$1,169.80