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	$97.28	3.150%	$100.3443	$100.34	$100.35	$100.30
Purchase #2	$72.25	13.529%	$82.0247	$82.02	$82.00	$82.00
Purchase #3	$156.30	9.109%	$170.5374	$170.54	$170.55	$170.50
Purchase #4	$74.89	4.271%	$78.0886	$78.09	$78.10	$78.10
Purchase #5	$159.38	6.659%	$169.9931	$169.99	$170.00	$170.00
Purchase #6	$190.52	4.392%	$198.8876	$198.89	$198.90	$198.90
Purchase #7	$156.91	13.559%	$178.1854	$178.19	$178.20	$178.20
7 purchase totals =	$907.53		$978.0611	$978.06	$978.10	$978.00