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	$243.76	12.614%	$274.5079	$274.51	$274.50	$274.50
Purchase #2	$97.95	10.158%	$107.8998	$107.90	$107.90	$107.90
Purchase #3	$30.51	13.215%	$34.5419	$34.54	$34.55	$34.50
Purchase #4	$20.37	6.660%	$21.7266	$21.73	$21.75	$21.70
Purchase #5	$98.32	11.803%	$109.9247	$109.92	$109.90	$109.90
Purchase #6	$157.28	11.826%	$175.8799	$175.88	$175.90	$175.90
Purchase #7	$115.27	6.735%	$123.0334	$123.03	$123.05	$123.00
7 purchase totals =	$763.46		$847.5142	$847.51	$847.55	$847.40