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	$80.72	10.333%	$89.0608	$89.06	$89.05	$89.10
Purchase #2	$66.79	11.371%	$74.3847	$74.38	$74.40	$74.40
Purchase #3	$223.85	10.111%	$246.4835	$246.48	$246.50	$246.50
Purchase #4	$247.90	5.467%	$261.4527	$261.45	$261.45	$261.50
Purchase #5	$88.92	10.806%	$98.5287	$98.53	$98.55	$98.50
Purchase #6	$89.82	4.143%	$93.5412	$93.54	$93.55	$93.50
Purchase #7	$131.46	4.381%	$137.2193	$137.22	$137.20	$137.20
7 purchase totals =	$929.46		$1,000.6709	$1,000.66	$1,000.70	$1,000.70