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	$128.67	12.181%	$144.3433	$144.34	$144.35	$144.30
Purchase #2	$199.83	7.855%	$215.5266	$215.53	$215.55	$215.50
Purchase #3	$167.30	11.314%	$186.2283	$186.23	$186.25	$186.20
Purchase #4	$37.32	13.554%	$42.3784	$42.38	$42.40	$42.40
Purchase #5	$80.85	8.682%	$87.8694	$87.87	$87.85	$87.90
Purchase #6	$70.53	7.594%	$75.886	$75.89	$75.90	$75.90
Purchase #7	$83.97	6.453%	$89.3886	$89.39	$89.40	$89.40
7 purchase totals =	$768.47		$841.6206	$841.63	$841.70	$841.60