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	$48.54	4.790%	$50.8651	$50.87	$50.85	$50.90
Purchase #2	$201.93	6.665%	$215.3886	$215.39	$215.40	$215.40
Purchase #3	$131.64	13.461%	$149.3601	$149.36	$149.35	$149.40
Purchase #4	$55.75	10.794%	$61.7677	$61.77	$61.75	$61.80
Purchase #5	$106.77	6.391%	$113.5937	$113.59	$113.60	$113.60
Purchase #6	$75.25	3.669%	$78.0109	$78.01	$78.00	$78.00
Purchase #7	$75.36	9.539%	$82.5486	$82.55	$82.55	$82.50
7 purchase totals =	$695.24		$751.5347	$751.54	$751.50	$751.60