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	$65.57	11.653%	$73.2109	$73.21	$73.20	$73.20
Purchase #2	$105.45	7.637%	$113.5032	$113.50	$113.50	$113.50
Purchase #3	$79.88	3.219%	$82.4513	$82.45	$82.45	$82.50
Purchase #4	$189.96	13.401%	$215.4165	$215.42	$215.40	$215.40
Purchase #5	$206.28	8.809%	$224.4512	$224.45	$224.45	$224.50
Purchase #6	$73.39	10.150%	$80.8391	$80.84	$80.85	$80.80
Purchase #7	$90.89	10.612%	$100.5352	$100.54	$100.55	$100.50
7 purchase totals =	$811.42		$890.4074	$890.41	$890.40	$890.40