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	$87.63	13.736%	$99.6669	$99.67	$99.65	$99.70
Purchase #2	$176.66	8.648%	$191.9376	$191.94	$191.95	$191.90
Purchase #3	$147.53	4.262%	$153.8177	$153.82	$153.80	$153.80
Purchase #4	$111.98	9.588%	$122.7166	$122.72	$122.70	$122.70
Purchase #5	$164.67	12.670%	$185.5337	$185.53	$185.55	$185.50
Purchase #6	$85.35	6.120%	$90.5734	$90.57	$90.55	$90.60
Purchase #7	$109.48	4.781%	$114.7142	$114.71	$114.70	$114.70
7 purchase totals =	$883.30		$958.9601	$958.96	$958.90	$958.90