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	$63.94	11.647%	$71.3871	$71.39	$71.40	$71.40
Purchase #2	$79.95	6.488%	$85.1372	$85.14	$85.15	$85.10
Purchase #3	$133.51	12.785%	$150.5793	$150.58	$150.60	$150.60
Purchase #4	$78.49	11.524%	$87.5352	$87.54	$87.55	$87.50
Purchase #5	$121.55	4.761%	$127.337	$127.34	$127.35	$127.30
Purchase #6	$88.51	6.748%	$94.4827	$94.48	$94.50	$94.50
Purchase #7	$202.73	9.523%	$222.036	$222.04	$222.05	$222.00
7 purchase totals =	$768.68		$838.4945	$838.51	$838.60	$838.40