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	$150.64	3.861%	$156.4562	$156.46	$156.45	$156.50
Purchase #2	$112.64	5.391%	$118.7124	$118.71	$118.70	$118.70
Purchase #3	$130.85	6.160%	$138.9104	$138.91	$138.90	$138.90
Purchase #4	$85.50	5.140%	$89.8947	$89.89	$89.90	$89.90
Purchase #5	$148.55	13.122%	$168.0427	$168.04	$168.05	$168.00
Purchase #6	$49.57	9.655%	$54.356	$54.36	$54.35	$54.40
Purchase #7	$81.41	3.834%	$84.5313	$84.53	$84.55	$84.50
7 purchase totals =	$759.16		$810.9037	$810.90	$810.90	$810.90