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	$78.49	13.688%	$89.2337	$89.23	$89.25	$89.20
Purchase #2	$247.79	7.258%	$265.7746	$265.77	$265.75	$265.80
Purchase #3	$161.77	6.140%	$171.7027	$171.70	$171.70	$171.70
Purchase #4	$167.57	11.197%	$186.3328	$186.33	$186.35	$186.30
Purchase #5	$104.38	13.457%	$118.4264	$118.43	$118.45	$118.40
Purchase #6	$233.34	13.648%	$265.1862	$265.19	$265.20	$265.20
Purchase #7	$59.45	4.356%	$62.0396	$62.04	$62.05	$62.00
7 purchase totals =	$1,052.79		$1,158.6960	$1,158.69	$1,158.75	$1,158.60