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	$239.89	10.309%	$264.6203	$264.62	$264.60	$264.60
Purchase #2	$118.47	7.223%	$127.0271	$127.03	$127.05	$127.00
Purchase #3	$174.37	4.300%	$181.8679	$181.87	$181.85	$181.90
Purchase #4	$53.48	4.193%	$55.7224	$55.72	$55.70	$55.70
Purchase #5	$29.51	13.211%	$33.4086	$33.41	$33.40	$33.40
Purchase #6	$75.83	11.747%	$84.7378	$84.74	$84.75	$84.70
Purchase #7	$104.69	4.646%	$109.5539	$109.55	$109.55	$109.60
7 purchase totals =	$796.24		$856.9380	$856.94	$856.90	$856.90